Fixes in the logic for dismissing the GestureNav overlay.
- Added the logic to keep track of the 'target' web page and the current web page in OverscrollNavigationOverlay so that the overlay is not dismissed prematurely when navigating through multiple pages.
- For the purposes of the overlay - consider the page 'loaded' once the main frame is loaded, so that we don't have to wait for the entire page to load. This saves us up to 300ms for complex pages with multiple iframes.
BUG=345380, 347235
Review URL: https://codereview.chromium.org/
178343008
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256076 0039d316-1c4b-4281-b951-d872f2087c98