Convert Android WebView manifest overlays to C++

Removes JSON manifest overlays from android_webview/browser and
replaces them with C++ Manifest object definitions.

TBR: estade@chromium.org
Bug: 895616
Change-Id: I7fb46141f9c43349cf4b98011014eaea7b717eab
Reviewed-on: https://chromium-review.googlesource.com/c/1404750
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623766}
14 files changed