See https://uberchromegw.corp.google.com/i/chromium.android/builders/Android%20Cronet%20Data%20Reduction%20Proxy%20Builder/builds/4237

Culprit CL is almost certainly https://codereview.chromium.org/2692203007 "Add PrefStore::GetValues", I'll revert.

[3960/7201] CXX obj/components/cronet/android/cronet_static/cronet_data_reduction_proxy.o
FAILED: obj/components/cronet/android/cronet_static/cronet_data_reduction_proxy.o 
/b/build/slave/cache/goma_client/gomacc ../../third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++ -MMD -MF obj/components/cronet/android/cronet_static/cronet_data_reduction_proxy.o.d -DDATA_REDUCTION_PROXY_SUPPORT -DV8_DEPRECATION_WARNINGS -DUSE_OPENSSL_CERTS=1 -DNO_TCMALLOC -DUSE_EXTERNAL_POPUP_MENU=1 -DDISABLE_NACL -DSAFE_BROWSING_DB_REMOTE -DCHROMIUM_BUILD -DENABLE_MEDIA_ROUTER=1 -DENABLE_WEBVR -DFIELDTRIAL_TESTING_ENABLED -D_FILE_OFFSET_BITS=64 -DANDROID -DHAVE_SYS_UIO_H -DANDROID_NDK_VERSION=r12b -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D_FORTIFY_SOURCE=2 -D__GNU_SOURCE=1 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DHAVE_PTHREAD -Igen/components/cronet/android/cronet_version_header -I../.. -Igen -I../../third_party/protobuf/src -Igen/protoc_out -I../../third_party/protobuf/src -Igen/components/cronet/android/cronet_jni_headers -Igen/components/cronet/android/cronet_jni_headers/cronet -Igen/components/metrics/proto -I../../third_party/boringssl/src/include -DLOGGING=1 -Wno-sign-promo -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -pipe -ffunction-sections -fno-short-enums -finline-limit=64 -march=armv7-a -mfloat-abi=softfp -mtune=generic-armv7-a -fno-tree-sra -fno-caller-saves -mfpu=vfpv3-d16 -mthumb -mthumb-interwork -Wall -Werror -Wno-psabi -Wno-unused-local-typedefs -Wno-maybe-uninitialized -Wno-missing-field-initializers -Wno-unused-parameter -Os -fno-ident -fdata-sections -ffunction-sections -fomit-frame-pointer -gdwarf-3 -g1 --sysroot=../../third_party/android_tools/ndk/platforms/android-16/arch-arm -fvisibility=hidden -fvisibility-inlines-hidden -std=gnu++11 -Wno-narrowing -fno-rtti -isystem../../third_party/android_tools/ndk/sources/cxx-stl/llvm-libc++/libcxx/include -isystem../../third_party/android_tools/ndk/sources/cxx-stl/llvm-libc++abi/libcxxabi/include -isystem../../third_party/android_tools/ndk/sources/android/support/include -fno-exceptions -c ../../components/cronet/android/cronet_data_reduction_proxy.cc -o obj/components/cronet/android/cronet_static/cronet_data_reduction_proxy.o
../../components/cronet/android/cronet_data_reduction_proxy.cc: In function 'std::__ndk1::unique_ptr<PrefService> cronet::{anonymous}::CreatePrefService()':
../../components/cronet/android/cronet_data_reduction_proxy.cc:43:54: error: invalid new-expression of abstract class type 'CronetInMemoryPrefStore'
       make_scoped_refptr(new CronetInMemoryPrefStore()));
                                                      ^
In file included from ../../components/cronet/android/cronet_data_reduction_proxy.cc:13:0:
../../components/cronet/android/cronet_in_memory_pref_store.h:26:7: note:   because the following virtual functions are pure within 'CronetInMemoryPrefStore':
 class CronetInMemoryPrefStore : public PersistentPrefStore {
       ^
In file included from ../../components/prefs/writeable_pref_store.h:14:0,
                 from ../../components/prefs/persistent_pref_store.h:11,
                 from ../../components/cronet/android/cronet_in_memory_pref_store.h:16,
                 from ../../components/cronet/android/cronet_data_reduction_proxy.cc:13:
../../components/prefs/pref_store.h:58:50: note: 	virtual std::__ndk1::unique_ptr<base::DictionaryValue> PrefStore::GetValues() const
   virtual std::unique_ptr<base::DictionaryValue> GetValues() const = 0;