GitLab

This CL adds a WebUI for App Management that replaces chrome://apps
when the feature NewAppManagement is enabled. This involves:
- adding the feature
- adding a new MojoWebUIController
- adding a mojom, and its C++ handler
- adding a skeleton HTML and Polymer 'app' element
- adding a BrowserProxy which connects the Renderer JS to the backend C++.

Bug: 906508
Change-Id: Iac5be9ce82dc2cb0b1c77301ca43ccf7a99f318f
Reviewed-on: https://chromium-review.googlesource.com/c/1309380
Commit-Queue: calamity <calamity@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609204}