[Android WebView] Fix assertion failure in WindowAndroid.

Ensure that AwContents is meeting the expectations of WindowAndroid
and provides it an ApplicationContext.

Additionally, fix indentation in AwContents.

Review URL: https://codereview.chromium.org/88683003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237411 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237411