Treat voice searches from within the browser differently

Treat voice searches from within the browser differently
from those initiated from outside the browser.

Fix for http://b/issue?id=2546173

For a voice search initiated from outside the browser, an appId
will be attached.  In that case, try to reuse the application tab.
In TabControl.recreateWebView, treat this as if the url does not
match the old url, so a new WebView will be created with a fresh
history list, and the back key will exit the browser.  However, if
no appId is provided, simply reuse the current tab.  In this case,
the history list will be preserved, and pressing the back key will
return to earlier voice searches.

Change-Id: I9ec1efd56454ba94eb2bc348c4476fb6bd025dad