Do V8 GC ASAP if system memory is pressured
Currently after receiving memory pressure notification, Chrome posts
asynchronous task to renderer main thread to trigger V8 GC. If renderer
main thread is busy, purging memory task will be postponed running,
which increases OOM risk.
The CL can send memory pressure notification to renderer main thread
synchronously and trigger V8 GC while V8 is in the middle of executing
JavaScript.
The CL depends on CL 1813963002
BUG=590975
Review-Url: https://codereview.chromium.org/1749073002
Cr-Commit-Position: refs/heads/master@{#391167}
8 files changed
