It seems to pass on its own, but fails when run along with other tests:

$ webkit_unit_tests --gtest_filter='ScrollAnchorTest.*'
IMPORTANT DEBUGGING NOTE: batches of tests are run inside their
own process. For debugging a test inside a debugger, use the
--gtest_filter=<your_test_name> flag along with
--single-process-tests.
Using sharding settings from environment. This is shard 0/1
Using 1 parallel jobs.
Note: Google Test filter = ScrollAnchorTest.Basic:ScrollAnchorTest.FractionalOffsetsAreRoundedBeforeComparing:ScrollAnchorTest.UMAMetricUpdated:ScrollAnchorTest.AnchorWithLayerInScrollingDiv:ScrollAnchorTest.FullyContainedInlineBlock:ScrollAnchorTest.TextBounds:ScrollAnchorTest.ExcludeFixedPosition:ScrollAnchorTest.ExcludeAbsolutePosition
[==========] Running 8 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 8 tests from ScrollAnchorTest
[ RUN      ] ScrollAnchorTest.Basic
[       OK ] ScrollAnchorTest.Basic (80 ms)
[ RUN      ] ScrollAnchorTest.FractionalOffsetsAreRoundedBeforeComparing
[       OK ] ScrollAnchorTest.FractionalOffsetsAreRoundedBeforeComparing (6 ms)
[ RUN      ] ScrollAnchorTest.UMAMetricUpdated
../../base/test/histogram_tester.cc:42: Failure
Expected: (static_cast<base::HistogramBase*>(__null)) != (histogram), actual: NULL vs NULL
Histogram "Layout.ScrollAnchor.AdjustedScrollOffset" does not exist.
[  FAILED  ] ScrollAnchorTest.UMAMetricUpdated (5 ms)
[ RUN      ] ScrollAnchorTest.AnchorWithLayerInScrollingDiv
[       OK ] ScrollAnchorTest.AnchorWithLayerInScrollingDiv (7 ms)
[ RUN      ] ScrollAnchorTest.FullyContainedInlineBlock
[       OK ] ScrollAnchorTest.FullyContainedInlineBlock (6 ms)
[ RUN      ] ScrollAnchorTest.TextBounds
[       OK ] ScrollAnchorTest.TextBounds (13 ms)
[ RUN      ] ScrollAnchorTest.ExcludeFixedPosition
[       OK ] ScrollAnchorTest.ExcludeFixedPosition (7 ms)
[ RUN      ] ScrollAnchorTest.ExcludeAbsolutePosition
[       OK ] ScrollAnchorTest.ExcludeAbsolutePosition (9 ms)
[----------] 8 tests from ScrollAnchorTest (134 ms total)

[----------] Global test environment tear-down
[==========] 8 tests from 1 test case ran. (135 ms total)
[  PASSED  ] 7 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] ScrollAnchorTest.UMAMetricUpdated

 1 FAILED TEST
[0512/145031:ERROR:kill_posix.cc(82)] Unable to terminate process group 28152: No such process
[1/8] ScrollAnchorTest.Basic (80 ms)
[2/8] ScrollAnchorTest.FractionalOffsetsAreRoundedBeforeComparing (6 ms)
[3/8] ScrollAnchorTest.UMAMetricUpdated (5 ms)
[4/8] ScrollAnchorTest.AnchorWithLayerInScrollingDiv (7 ms)
[5/8] ScrollAnchorTest.FullyContainedInlineBlock (6 ms)
[6/8] ScrollAnchorTest.TextBounds (13 ms)
[7/8] ScrollAnchorTest.ExcludeFixedPosition (7 ms)
[8/8] ScrollAnchorTest.ExcludeAbsolutePosition (9 ms)
1 test failed:
    ScrollAnchorTest.UMAMetricUpdated (../../third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp:104)
Tests took 0 seconds.