Add test image data for extensions ImageLoaderTest

This must be dcommit'd because CQ corrupts PNG files when landing them.
crbug.com/339068

BUG=none
TEST=none
R=rockot@chromium.org
TBR=rockot@chromium.org

Review URL: https://codereview.chromium.org/424123004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287552 0039d316-1c4b-4281-b951-d872f2087c98

extensions/test/data/image_loader/manifest.json

+{
+  "name": "test",
+  "version": "1",
+  "manifest_version": 2,
+  "icons": { "16": "16.png",
+             "24": "24.png" }
+}