components_unittests failing on chromium.memory/Linux CFI

Builders failed on: 
- Linux CFI: 
  https://build.chromium.org/p/chromium.memory/builders/Linux%20CFI

Last known good: r500362
First known bad: r500370

4 tests crashed:
    PrefetchDownloadFlowTest.DelayRunningDownloadCleanupTask (../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:176)
    PrefetchDownloadFlowTest.DownloadServiceReadyAfterPrefetchSystemReady (../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:100)
    PrefetchDownloadFlowTest.DownloadServiceReadyBeforePrefetchSystemReady (../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:129)
    PrefetchDownloadFlowTest.DownloadServiceUnavailable (../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:152)

Certainly caused by r500369, which introduced these tests.

Full stdout:

[ RUN      ] PrefetchDownloadFlowTest.DownloadServiceUnavailable
../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12: runtime error: control flow integrity check for type 'offline_pages::TestPrefetchDispatcher' failed during base-to-derived cast (vtable address 0x000000ba5820)
0x000000ba5820: note: vtable is of type 'offline_pages::PrefetchDispatcherImpl'
 00 00 00 00  70 1c d3 0b 00 00 00 00  50 1d d3 0b 00 00 00 00  80 1d d3 0b 00 00 00 00  20 1e d3 0b
              ^
    #0 0x5998a0d in offline_pages::PrefetchDownloadFlowTest::prefetch_dispatcher() const components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12
    #1 0x599904c in offline_pages::PrefetchDownloadFlowTest_DownloadServiceUnavailable_Test::TestBody() components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:166:3
    #2 0x5fed743 in testing::Test::Run() third_party/googletest/src/googletest/src/gtest.cc:2472:5
    #3 0x5fedfed in testing::TestInfo::Run() third_party/googletest/src/googletest/src/gtest.cc:2654:11
    #4 0x5fee841 in testing::TestCase::Run() third_party/googletest/src/googletest/src/gtest.cc:2772:28
    #5 0x5ff3ba2 in testing::internal::UnitTestImpl::RunAllTests() third_party/googletest/src/googletest/src/gtest.cc:4677:43
    #6 0x5ff386c in testing::UnitTest::Run() third_party/googletest/src/googletest/src/gtest.cc:4285:10
    #7 0x931f7dc in base::TestSuite::Run() base/test/test_suite.cc:270:16
    #8 0x9322dbf in base::(anonymous namespace)::LaunchUnitTestsInternal(base::RepeatingCallback<int ()> const&, unsigned long, int, bool, base::RepeatingCallback<void ()> const&) base/test/launcher/unit_test_launcher.cc:216:27
    #9 0x9322c88 in base::LaunchUnitTests(int, char**, base::RepeatingCallback<int ()> const&) base/test/launcher/unit_test_launcher.cc:475:10
    #10 0x563d70c in main components/test/run_all_unittests.cc:8:10
    #11 0x7f41975f9f44 in __libc_start_main /build/eglibc-SvCtMH/eglibc-2.19/csu/libc-start.c:287:0
    #12 0x3ff6028 in _start ??:0:0
[11412/11415] PrefetchDownloadFlowTest.DownloadServiceUnavailable (CRASHED)
[ RUN      ] PrefetchDownloadFlowTest.DownloadServiceReadyBeforePrefetchSystemReady
../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12: runtime error: control flow integrity check for type 'offline_pages::TestPrefetchDispatcher' failed during base-to-derived cast (vtable address 0x000000ba5820)
0x000000ba5820: note: vtable is of type 'offline_pages::PrefetchDispatcherImpl'
 00 00 00 00  70 1c d3 0b 00 00 00 00  50 1d d3 0b 00 00 00 00  80 1d d3 0b 00 00 00 00  20 1e d3 0b
              ^
    #0 0x5998a0d in offline_pages::PrefetchDownloadFlowTest::prefetch_dispatcher() const components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12
    #1 0x5998b50 in offline_pages::PrefetchDownloadFlowTest_DownloadServiceReadyBeforePrefetchSystemReady_Test::TestBody() components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:142:3
    #2 0x5fed743 in testing::Test::Run() third_party/googletest/src/googletest/src/gtest.cc:2472:5
    #3 0x5fedfed in testing::TestInfo::Run() third_party/googletest/src/googletest/src/gtest.cc:2654:11
    #4 0x5fee841 in testing::TestCase::Run() third_party/googletest/src/googletest/src/gtest.cc:2772:28
    #5 0x5ff3ba2 in testing::internal::UnitTestImpl::RunAllTests() third_party/googletest/src/googletest/src/gtest.cc:4677:43
    #6 0x5ff386c in testing::UnitTest::Run() third_party/googletest/src/googletest/src/gtest.cc:4285:10
    #7 0x931f7dc in base::TestSuite::Run() base/test/test_suite.cc:270:16
    #8 0x9322dbf in base::(anonymous namespace)::LaunchUnitTestsInternal(base::RepeatingCallback<int ()> const&, unsigned long, int, bool, base::RepeatingCallback<void ()> const&) base/test/launcher/unit_test_launcher.cc:216:27
    #9 0x9322c88 in base::LaunchUnitTests(int, char**, base::RepeatingCallback<int ()> const&) base/test/launcher/unit_test_launcher.cc:475:10
    #10 0x563d70c in main components/test/run_all_unittests.cc:8:10
    #11 0x7ff7427d1f44 in __libc_start_main /build/eglibc-SvCtMH/eglibc-2.19/csu/libc-start.c:287:0
    #12 0x3ff6028 in _start ??:0:0
[11413/11415] PrefetchDownloadFlowTest.DownloadServiceReadyBeforePrefetchSystemReady (CRASHED)
[ RUN      ] PrefetchDownloadFlowTest.DownloadServiceReadyAfterPrefetchSystemReady
../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12: runtime error: control flow integrity check for type 'offline_pages::TestPrefetchDispatcher' failed during base-to-derived cast (vtable address 0x000000ba5820)
0x000000ba5820: note: vtable is of type 'offline_pages::PrefetchDispatcherImpl'
 00 00 00 00  70 1c d3 0b 00 00 00 00  50 1d d3 0b 00 00 00 00  80 1d d3 0b 00 00 00 00  20 1e d3 0b
              ^
    #0 0x5998a0d in offline_pages::PrefetchDownloadFlowTest::prefetch_dispatcher() const components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12
    #1 0x599858e in offline_pages::PrefetchDownloadFlowTest_DownloadServiceReadyAfterPrefetchSystemReady_Test::TestBody() components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:109:3
    #2 0x5fed743 in testing::Test::Run() third_party/googletest/src/googletest/src/gtest.cc:2472:5
    #3 0x5fedfed in testing::TestInfo::Run() third_party/googletest/src/googletest/src/gtest.cc:2654:11
    #4 0x5fee841 in testing::TestCase::Run() third_party/googletest/src/googletest/src/gtest.cc:2772:28
    #5 0x5ff3ba2 in testing::internal::UnitTestImpl::RunAllTests() third_party/googletest/src/googletest/src/gtest.cc:4677:43
    #6 0x5ff386c in testing::UnitTest::Run() third_party/googletest/src/googletest/src/gtest.cc:4285:10
    #7 0x931f7dc in base::TestSuite::Run() base/test/test_suite.cc:270:16
    #8 0x9322dbf in base::(anonymous namespace)::LaunchUnitTestsInternal(base::RepeatingCallback<int ()> const&, unsigned long, int, bool, base::RepeatingCallback<void ()> const&) base/test/launcher/unit_test_launcher.cc:216:27
    #9 0x9322c88 in base::LaunchUnitTests(int, char**, base::RepeatingCallback<int ()> const&) base/test/launcher/unit_test_launcher.cc:475:10
    #10 0x563d70c in main components/test/run_all_unittests.cc:8:10
    #11 0x7f399906af44 in __libc_start_main /build/eglibc-SvCtMH/eglibc-2.19/csu/libc-start.c:287:0
    #12 0x3ff6028 in _start ??:0:0
[11414/11415] PrefetchDownloadFlowTest.DownloadServiceReadyAfterPrefetchSystemReady (CRASHED)
[ RUN      ] PrefetchDownloadFlowTest.DelayRunningDownloadCleanupTask
../../components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12: runtime error: control flow integrity check for type 'offline_pages::TestPrefetchDispatcher' failed during base-to-derived cast (vtable address 0x000000ba5820)
0x000000ba5820: note: vtable is of type 'offline_pages::PrefetchDispatcherImpl'
 00 00 00 00  70 1c d3 0b 00 00 00 00  50 1d d3 0b 00 00 00 00  80 1d d3 0b 00 00 00 00  20 1e d3 0b
              ^
    #0 0x5998a0d in offline_pages::PrefetchDownloadFlowTest::prefetch_dispatcher() const components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:85:12
    #1 0x5999566 in offline_pages::PrefetchDownloadFlowTest_DelayRunningDownloadCleanupTask_Test::TestBody() components/offline_pages/core/prefetch/prefetch_download_flow_unittest.cc:198:3
    #2 0x5fed743 in testing::Test::Run() third_party/googletest/src/googletest/src/gtest.cc:2472:5
    #3 0x5fedfed in testing::TestInfo::Run() third_party/googletest/src/googletest/src/gtest.cc:2654:11
    #4 0x5fee841 in testing::TestCase::Run() third_party/googletest/src/googletest/src/gtest.cc:2772:28
    #5 0x5ff3ba2 in testing::internal::UnitTestImpl::RunAllTests() third_party/googletest/src/googletest/src/gtest.cc:4677:43
    #6 0x5ff386c in testing::UnitTest::Run() third_party/googletest/src/googletest/src/gtest.cc:4285:10
    #7 0x931f7dc in base::TestSuite::Run() base/test/test_suite.cc:270:16
    #8 0x9322dbf in base::(anonymous namespace)::LaunchUnitTestsInternal(base::RepeatingCallback<int ()> const&, unsigned long, int, bool, base::RepeatingCallback<void ()> const&) base/test/launcher/unit_test_launcher.cc:216:27
    #9 0x9322c88 in base::LaunchUnitTests(int, char**, base::RepeatingCallback<int ()> const&) base/test/launcher/unit_test_launcher.cc:475:10
    #10 0x563d70c in main components/test/run_all_unittests.cc:8:10
    #11 0x7f7df58f5f44 in __libc_start_main /build/eglibc-SvCtMH/eglibc-2.19/csu/libc-start.c:287:0
    #12 0x3ff6028 in _start ??:0:0
[11415/11415] PrefetchDownloadFlowTest.DelayRunningDownloadCleanupTask (CRASHED)