Add flag to WebView apks specifying that these apks contain WebView.
Add flag to WebView apks specifying that these apks contain WebView.

Add a flag to the WebView manifest to ensure that webview apks are
compatible with the new mechanism for loading webview.

BUG=476885

Review URL: https://codereview.chromium.org/1075883002

Cr-Commit-Position: refs/heads/master@{#324418}
(cherry picked from commit 3ad3685b582529a24f5875f7346bf0c39335d5e9)

R=gsennton@chromium.org

Review URL: https://codereview.chromium.org/1085863003

Cr-Commit-Position: fe94940391158563b8e4cf7888f93321f554af93@{#84}
Cr-Branched-From: 9fdd9ec11ee753dedeffe15e7e822b13445dc287@{#323860}

fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk