Remove TabContents from TabStripModelObserver::TabDetachedAt.

BUG=107201
TEST=no visible change


Review URL: https://chromiumcodereview.appspot.com/11293205

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@167122 0039d316-1c4b-4281-b951-d872f2087c98
void PageSnapshotTaker::Start() {
  AutomationTabHelper* automation_tab_helper =
      AutomationTabHelper::FromWebContents(tab_contents_->web_contents());
  StartObserving(automation_tab_helper);
  automation_tab_helper->SnapshotEntirePage();
}

void PageSnapshotTaker::Start() {
  AutomationTabHelper* automation_tab_helper =
      AutomationTabHelper::FromWebContents(tab_contents_->web_contents());
  StartObserving(automation_tab_helper);
  automation_tab_helper->SnapshotEntirePage();
}
