Change serialization for SVG resource url(...)'s

For non-local URLs, serialize the absolute form.

Reduce the AtomicString <-> String impedance while at it.

Bug: 842665
Change-Id: Ibc7804eeb6436d32202915e20e612b7bb5cf6b94
Reviewed-on: https://chromium-review.googlesource.com/1213175
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#591627}
13 files changed