[android_webview] Call onPageFinished for anchor navigations.

This makes the android_webview call onPageFinished for navigations
which only result in the hash fragment being changed. This bug was
introduced when we switched from didStopLoading to didFinishLoad.

BUG=341085, 291747

Review URL: https://codereview.chromium.org/139493008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249142 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249142