"Browser: Update BrowserPreferencesPage to Override isValidFragment()"

Override isValidFragment to avoid the crash when browser
settings is accessed.

Change-Id: Ide16b95781b186928bf804dd3bee7bbf6841bafd
CRs-Fixed: 725502
Always show the action bar overflow

As with native action bars.

Change-Id: I460ee02b370d7f220a8702d2e7644a7c775e3b21
Reimplement titlebar autohiding to be compatible with chromium webview.

Patch Set 4: Fix code formatting

Change-Id: I4de873f7c089d4f7dede944d05f48d03000f3d99