[Files.app] Fix the test failure due to r232408
r232408 caused ExtensionIconManagerTest.LoadComponentExtensionResource failure
although r232408 fixed ImageLoaderTest.IsComponentExtensionResource.
This CL fixes it as well as ImageLoaderTest.IsComponentExtensionResource.
BUG=none
TEST=manually tested
NOTRY=True
R=yoshiki@chromium.org
TBR=csharp@chromium.org, yoshiki@chromium.org
Review URL: https://codereview.chromium.org/
56303003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232447 0039d316-1c4b-4281-b951-d872f2087c98