M56: Messaging: Fix crash when MessagePort is closed while messages are queued

M56: Messaging: Fix crash when MessagePort is closed while messages are queued

dispatchMessages() did a check at the start of function for m_closed, but it
then looped over queued messages and dispatched each one. Each dispatch causes
the onmessage handler to run, which can trigger closing the execution context.
Since https://crrev.com/9c675cfdcf006e5ca978b0dfa04f187ed36f86cc, getExecutionContext()
would then return null and crash. Since close() is called when the execution
context dies and possibly in other cases, check |m_closed| before each dispatch.

BUG=649616
Review-Url: https://codereview.chromium.org/2533323003
Cr-Commit-Position: refs/heads/master@{#435190}
(cherry picked from commit 6ec0c90214ba34ce39e4224561235b7142d07eaa)

Committed: https://chromium.googlesource.com/chromium/src/+/b99d81b8ddc75ccbfdd0a2b1cefeec3a32af0221

[falken, 2016-12-05 05:38:14]

Description was changed from

==========
M56: Messaging: Fix crash when MessagePort is closed while messages are queued

dispatchMessages() did a check at the start of function for m_closed, but it
then looped over queued messages and dispatched each one. Each dispatch causes
the onmessage handler to run, which can trigger closing the execution context.
Since https://crrev.com/9c675cfdcf006e5ca978b0dfa04f187ed36f86cc,
getExecutionContext()
would then return null and crash. Since close() is called when the execution
context dies and possibly in other cases, check |m_closed| before each dispatch.

BUG=649616

Review-Url: https://codereview.chromium.org/2533323003
Cr-Commit-Position: refs/heads/master@{#435190}
(cherry picked from commit 6ec0c90214ba34ce39e4224561235b7142d07eaa)
==========

to

==========
M56: Messaging: Fix crash when MessagePort is closed while messages are queued

dispatchMessages() did a check at the start of function for m_closed, but it
then looped over queued messages and dispatched each one. Each dispatch causes
the onmessage handler to run, which can trigger closing the execution context.
Since https://crrev.com/9c675cfdcf006e5ca978b0dfa04f187ed36f86cc,
getExecutionContext()
would then return null and crash. Since close() is called when the execution
context dies and possibly in other cases, check |m_closed| before each dispatch.

BUG=649616

Review-Url: https://codereview.chromium.org/2533323003
Cr-Commit-Position: refs/heads/master@{#435190}
(cherry picked from commit 6ec0c90214ba34ce39e4224561235b7142d07eaa)

Committed:
https://chromium.googlesource.com/chromium/src/+/b99d81b8ddc75ccbfdd0a2b1cefe...
==========

[falken, 2016-12-05 05:38:15]

Committed patchset #1 (id:1) manually as
b99d81b8ddc75ccbfdd0a2b1cefeec3a32af0221.