Triage: Routing to erikchen@ for the hotkey usage.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8f2f9568808ee117698e0a9008a0b52902d2363e

commit 8f2f9568808ee117698e0a9008a0b52902d2363e
Author: Erik Chen <erikchen@chromium.org>
Date: Fri Jun 08 00:44:54 2018

Unification of macOS keyEquivalent (hotkey) handling.

This CL makes the CommandDispatcher class responsible for all NSMenu-related
keyEquivalent handling. The logic is now shared by both Views and Cocoa. This
fixes many Views bugs, and some Cocoa bugs.

Previously, there several different pieces of logic for handling NSMenu-related
keyEquivalents.

* If a RenderWidgetHostViewCocoa was the firstResponder, then all the logic in
  CommandDispatcher was skipped.
  * In both Cocoa and Views, there was logic in content/ via RenderWidget*
    classes that would short-circuit but also fail to handle the keyEquivalent.
    [e.g. if renderer process was killed].
    * In Cocoa, content/ would call into
      BrowserWindowCocoa::PreHandleKeyboardEvent(). This had mostly the right
      behavior, except it missed out on edge-case logic in CommandDispatcher.
    * In Views, content/ would call into BrowserView::PreHandleKeyboardEvent.
      This relied on AcceleratorTable to lookup the command for a keyEquivalent.
      This entire class is unusable for keyEquivalents because it holds a static
      mapping, whereas on macOS, the mapping is user configurable and dynamic.
  * If the hotkey was not immediately consumed, it would be passed to the
    renderer process. If the renderer process chose not to consume the hotkey,
    the browser process would get it again.
    * In Cocoa, the event would be redispatched to CommandDispatcher. This had
      the right behavior.
    * In Views, the event would be sent to AcceleratorTable again, once again
      having the wrong behavior.
* If any other class was firstResponder, then the logic in CommandDispatcher
  would trigger.

This CL makes CommandDispatcher the only place to handle NSMenu-related
keyEquivalents. This allows us to centralize the logic, including workarounds.

New logic:

* The CommandDispatcherDelegate is given an opportunity to process the
  keyEquivalent via prePerformKeyEquivalent:. If the keyEquivalent is reserved
  by the browser, it is immediately handled.
* Next, the firstResponder is given a chance to process the keyEquivalent. If
  the firstResponder is a RenderWidgetHostViewCocoa, this goes through the same
  code paths as above, except BrowserWindowCocoa::PreHandleKeyboardEvent() is
  mostly a no-op.
* Then, the CommandDispatcherDelegate gets another chance to process the
  keyEquivalent via postPerformKeyEquivalent:.

If the firstResponder was a RenderWidgetHostViewCocoa which asynchronously chose
to not process the event, then both Cocoa and Views will take the returning
event and call redispatchEvent:, which will also call into
-[CommandDispatcherDelegate postPerformKeyEquivalent:].

Change-Id: If724e125c6acf64ddd9f1d9cc296e761ffb2a886
Bug:  846893 ,  836947 ,  845465 ,  47134 
Reviewed-on: https://chromium-review.googlesource.com/1082818
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565490}
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