Use ChildThreadImpl::thread_safe_sender in font proxy if available

Use ChildThreadImpl::thread_safe_sender in font proxy if available

This changes the logic that the font proxy uses to get the IPC
sender. It will now try to get a sender in the initialization code,
and use that one if available. This allows it to get the sender
while it is still running on the main thread in the plugin, so that
it can use it for IPCs later when called from a different thread.
This is a threading violation, but it will allow the proxy to work
when called by Flash from a background thread.

BUG=631254
Review-Url: https://codereview.chromium.org/2182213004
Cr-Commit-Position: refs/heads/master@{#408551}
(cherry picked from commit ddaf9994ab75ff143da0c2f5c44499e49db1815f)

Committed: https://chromium.googlesource.com/chromium/src/+/b7b20301c408b1d22395353e68ee8887aac06d0a

[Ilya Kulshin, 2016-08-01 19:04:56]

Description was changed from

==========
Use ChildThreadImpl::thread_safe_sender in font proxy if available

This changes the logic that the font proxy uses to get the IPC
sender. It will now try to get a sender in the initialization code,
and use that one if available. This allows it to get the sender
while it is still running on the main thread in the plugin, so that
it can use it for IPCs later when called from a different thread.
This is a threading violation, but it will allow the proxy to work
when called by Flash from a background thread.

BUG=631254

Review-Url: https://codereview.chromium.org/2182213004
Cr-Commit-Position: refs/heads/master@{#408551}
(cherry picked from commit ddaf9994ab75ff143da0c2f5c44499e49db1815f)
==========

to

==========
Use ChildThreadImpl::thread_safe_sender in font proxy if available

This changes the logic that the font proxy uses to get the IPC
sender. It will now try to get a sender in the initialization code,
and use that one if available. This allows it to get the sender
while it is still running on the main thread in the plugin, so that
it can use it for IPCs later when called from a different thread.
This is a threading violation, but it will allow the proxy to work
when called by Flash from a background thread.

BUG=631254

Review-Url: https://codereview.chromium.org/2182213004
Cr-Commit-Position: refs/heads/master@{#408551}
(cherry picked from commit ddaf9994ab75ff143da0c2f5c44499e49db1815f)

Committed:
https://chromium.googlesource.com/chromium/src/+/b7b20301c408b1d22395353e68ee...
==========

[Ilya Kulshin, 2016-08-01 19:04:57]

Committed patchset #1 (id:1) manually as
b7b20301c408b1d22395353e68ee8887aac06d0a.