MIPS32r2: Fix Chromium runtime crash
Crash is caused by ldxc1 instruction, which traps when double values are
not aligned on 8-byte boundaries. Problem was tracked to SkChunkAlloc which
produces pointers aligned on 4-byte boundaries leading to misalignment.
This change makes sure that SkChunkAlloc will produce pointers that are
aligned to 8 bytes.
Appropriate tests are added to tests/MemsetTest.cpp
TEST=Build Chromium with Clang and run on MIPS32r2 platform
TEST=./out/Debug/dm --match Memset
BUG=130022
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Review-Url: https://codereview.chromium.org/
1849183004