GetHelp: Add missing permission "metricsPrivate" in manifest.json

BUG=349863
TEST=manual

Review URL: https://codereview.chromium.org/188573002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255480 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255480
Remove --ui-prioritize-in-gpu-process

It is already always on on Android and Chrome OS. Consensus is that we should
turn on on all Aura platform. The flag is a noop on other platforms.

BUG=344083

Review URL: https://codereview.chromium.org/183883023

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255481 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255481