Add ios/web/ test data for PNG favicon

This will be used by the next portion of ios/web/ code being upstreamed;
separating into another CL since it contains a binary file.

BUG=464810
R=eugenebut@chromium.org

Review URL: https://codereview.chromium.org/1108373003

Cr-Commit-Position: refs/heads/master@{#327329}

ios/web/ios_web_unittests.gyp

@@ -49,6 +49,7 @@
             'test_data_files': [
               'test/data/chrome.html',
               'test/data/testbadpass.pkpass',
+              'test/data/testfavicon.png',
               'test/data/testpass.pkpass',
             ],
             'test_data_prefix': 'ios/web',