app_list/chromeos: Fix wrong app icon in search results.
- Use match type to find extension app result;
- Load app icon using ImageLoadingTracker;
- Add a SearchResultObserver;
- SearchResultView implements SearchResultObserver to update when extension app
icon is loaded;
BUG=132361
TEST=Verify extension app icon shows up correctly in search results.
Review URL: https://chromiumcodereview.appspot.com/
10544116
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141865 0039d316-1c4b-4281-b951-d872f2087c98