Add IMMEDIATE_CRASH to measure how much V8 APIs return empty MaybeLocal handles

Add IMMEDIATE_CRASH to measure how much V8 APIs return empty MaybeLocal handles

Thanks to nhiroki's work, isolate->TerminateExecution was removed from common paths
of worker shutdown. Hence, it should be super rare that V8 APIs return empty MaybeLocal handles.
This CL adds IMMEDIATE_CRASH to measure how rare it is in the real world.

BUG=625512

[haraken, 2016-07-04 01:56:16]

haraken@chromium.org changed reviewers:
+ yukishiino@chromium.org

[haraken, 2016-07-04 01:56:16]

PTAL

[haraken, 2016-07-04 05:28:32]

It seems a lot of tests are failing. Looking.