Catch ManifestErrors with ErrorConsole; Add Browsertests

Add backend support for catching manifest install warnings with the ErrorConsole.  Forked from https://codereview.chromium.org/22938005 in order to reduce size and separate backend and frontend CLs.

BUG=21734

Review URL: https://chromiumcodereview.appspot.com/23684015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221020 0039d316-1c4b-4281-b951-d872f2087c98
13 files changed