Wrap all of the WebView Contexts

We're missing a few places in WebViewChromium and WebViewChromium where
we should be wrapping the application context. Particularly we need to
override getApplicationContext on ContextWrapper to return a wrapped
version.

Change-Id: Ic5a928f34c16cc86de331d39ce5eb534b2602907
Merge "Wrap all of the WebView Contexts" into chromium-dev