Adds virtual V8::Platform::OnCriticalMemoryPressure method, default
implementation does nothing.

Calls this method on first allocation failures in NewArray, Malloced,
and zone AccountingAllocator and adds retry logic.

Adds utility functions for allocating base::VirtualMemory to functions
in allocation.h, which call this method and add retry logic.

Calls these utility functions in heap CodeRange, Spaces, StoreBuffer
and SequentialMarkingDeque.

Bug: v8:6635
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I38afd394f3be556aca037d16675e9884658158cb
Reviewed-on: https://chromium-review.googlesource.com/583543
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46988}