Add a deprecation message for PPAPI WebSocket

Display a console message (in the context of the page) when a WebSocket
is created via the Pepper pp::WebSocket API.

Also add deprecation warnings to the documentation.

Tested by manual verification that the console message is shown when
the PPAPI WebSocket browser_tests are run.

Intent to deprecate thread:
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/3NYHaxhRs14/XOdUJBvHAwAJ

BUG=870586

Change-Id: Ib4631d11cd94cecad6c42e6b3fb1fb81ffc2b7fb
Reviewed-on: https://chromium-review.googlesource.com/1161712
Commit-Queue: Adam Rice <ricea@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#581191}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 77d2955c7480d8d51f31c82d512c944385279891
4 files changed