Add browser test for CustomizationWallpaperDownloader.
Also implements TestURLFetcher::SaveResponseToTemporaryFile(),
and explicitly allows ScopedIO in TestURLFetcher, as it doesn't support
asynchronous IO by design.
Note to tree sheriffs: this CL can break tests using FakeURLFetcherFactory.
BUG=366614
TEST=none
Review URL: https://codereview.chromium.org/253833006
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269907 0039d316-1c4b-4281-b951-d872f2087c98
12 files changed
