Allow chrome.debugger API to attach to extension background pages.

Since there is no way to provide a visual notification for the user this will be only possible when --remote-debugging-silent command line switch is present.

BUG=176962


Review URL: https://chromiumcodereview.appspot.com/12304021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@184645 0039d316-1c4b-4281-b951-d872f2087c98
14 files changed