[Background Fetch] Allow relative src paths with ImageResouce

Change-Id: I81a0ce6ebb664ec993028f561729051884924a26
Reviewed-on: https://chromium-review.googlesource.com/1152948
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Mugdha Lakhani <nator@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579780}
2 files changed