Add UMA stats for ExtensionCache

Reported metrics:
- number of extensions in cache
- size of cache on disk

BUG=316371
TEST=manual

Review URL: https://codereview.chromium.org/148013004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247760 0039d316-1c4b-4281-b951-d872f2087c98
BrowserPlugin: Allow stack to unwind before denying permission.

This prevents a use-after-free bug where it is possible WebContentsImpl attempts
to access a newly created window after BrowserPluginGuest has freed it because the
permission was instantly denied. This can happen if BrowserPluginGuest has no
delegate: it's not a <webview> or <adview>.

BUG=338345

Review URL: https://codereview.chromium.org/149643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247761 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247760
SVN changes up to revision 247761