Handle allocation failure with PartitionAllocReturnNull.
Handle allocation failure with PartitionAllocReturnNull.

if the browser is in OOM situation and PartitionAllocReturnNull is set,
it returns null instead of OOM crash.

BUG=374087

Review URL: https://codereview.chromium.org/295803005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@175091 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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