Extract UI dependencies from ExtensionHost, part 1

app_shell needs to support background pages in order to load apps, but doesn't
have the usual UI surfaces for Chrome extensions (popups, infobars, etc.).

* Extract functionality touching platform-specific views to ExtensionViewHost
* Remove references to panels, which don't use ExtensionHost

Reupload of LGTM'd change https://codereview.chromium.org/82163002 because
AppEngine is misbehaving.

BUG=321341
TEST=browser_tests, interactive_ui_tests
TBR=yoz@chromium.org

Review URL: https://codereview.chromium.org/86363003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237190 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237190
Modify the summaries of the UMAs Translate.DeclineTranslate(CloseInfobar)

Since the current summaries don't reflect the actual behavior, they should be fixed.

NOTRY=true

Review URL: https://codereview.chromium.org/85163002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237191 0039d316-1c4b-4281-b951-d872f2087c98
Remove --disable-batched-shutdown.

BUG=265764

Review URL: https://codereview.chromium.org/85203002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237192 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237192