macviews: switch back to Cocoa menus for Views context menus

This change:
1) Reverts erikchen@'s 79c8511fb8801f7fc23c4cbe81311b6065daef15, which removed
   the Cocoa menu runner code;
2) Wires the Cocoa menu runner code back up in MenuRunnerImplInterface::Create;
3) Fixes a latent bug in Textfield that could cause it to delete its context
   menu while handling a context menu activation - this is fine with Views menus
   but forbidden with Cocoa menus.

Bug: 860673
Change-Id: If110f09379c4661a4f61a8b0257cf5214503e6a9
Reviewed-on: https://chromium-review.googlesource.com/1131564
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574538}
7 files changed