Merge changes Ia26b07f0,Id3d2758c

* changes:
  Revert "Revert "Use the holder's gray bit in Baker read barrier slow paths (ARM, ARM64).""
  Revert "Revert "Use the "GC is marking" information in compiler read barriers (ARM, ARM64).""

diff --cc compiler/optimizing/code_generator_arm.cc
Simple merge

diff --cc compiler/optimizing/code_generator_arm.h
Simple merge

diff --cc compiler/optimizing/code_generator_arm64.cc
Simple merge

diff --cc compiler/optimizing/code_generator_arm64.h
Simple merge

diff --cc compiler/optimizing/code_generator_arm_vixl.cc
Simple merge

diff --cc compiler/optimizing/code_generator_arm_vixl.h
Simple merge