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This cl adds context menu to internal app at different places:
1. Add context menu to recommended searched results.
2. Add context menu to items in app list.
3. Add context menu to shelf items.

Bug: 824437
Test: new tests in AppContextMenuTest and LauncherContextMenuTest
Change-Id: I46a16b2a2b78d0027a3ce9a4f0afc94581e0c2b9
Reviewed-on: https://chromium-review.googlesource.com/1023042
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553338}