Removing the release-block label as this is just for a test. The actual fix is in stable now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/948fce0e3fb6866f24f2391cc2312a179b5ce421

commit 948fce0e3fb6866f24f2391cc2312a179b5ce421
Author: Ehsan Karamad <ekaramad@chromium.org>
Date: Fri Dec 08 16:38:07 2017

Add a test for misplaced drop down list in OOPIF-<webview> with offset form origin

This test is intended to catch regression such as the one reported in  https://crbug.com/772840 .

To support the API required by the test the following chances to content layer were required:

a) Add a helper class, RenderWidgetHostViewCocoaObserver to the public browser test utils which internally overrides the corresponding RWHVCocoa's methods and notifies the testobservers accordingly.

b) The class object of RednerWidgetHostViewCocoa is exposed in a public method. The class object is required for swizzling RWHVCococa methods.

Bug:  774986 
Change-Id: I44a09a8d62868f2048f8c35c2c1c9d56e53dd5a6
Reviewed-on: https://chromium-review.googlesource.com/809755
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522792}
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/chrome/browser/apps/guest_view/web_view_interactive_browsertest.cc
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/chrome/test/BUILD.gn
[add] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/chrome/test/data/extensions/platform_apps/web_view/shim/guest_with_select.html
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/chrome/test/data/extensions/platform_apps/web_view/shim/main.js
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/chrome/test/data/extensions/platform_apps/web_view/shim/manifest.json
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/content/browser/renderer_host/render_widget_host_view_mac.h
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/content/browser/renderer_host/render_widget_host_view_mac.mm
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/content/public/test/content_browser_test_utils.h
[modify] https://crrev.com/948fce0e3fb6866f24f2391cc2312a179b5ce421/content/public/test/content_browser_test_utils_mac.mm

Closing the bug since the test has landed.