Couple of minor changes to the WebKitAPI. This is a small step in a larger work-in-progress. See the bug for details.

* Distinguish more clearly between blobURLs and fileSystemURLs in WebBlobData and the very similar WebHTTPBody element structs.

* Put in place some of the new API to identify blob data by uuid instead of blob instances by URL. What's in place enough for Blink to call out to Chromium using the new id scheme. What's not in place is enough for Chrome to call into Blink using the new scheme as Blink doesn't know how to do that yet. Blink doesn't use the new API yet but Chromium is nearly ready for it to start doing so after https://codereview.chromium.org/23223003/ lands.

BUG=174200

Review URL: https://chromiumcodereview.appspot.com/23703003

git-svn-id: svn://svn.chromium.org/blink/trunk@157024 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Allow SVG images to animate their referenced image

This change makes SVG's <image> element have an animatable
href attribute. Previously, SVGImageElement::imageSourceURL()
returned the non-animating base attribute value but after
this change we return the animating value.

This change required changing the return type of imageSourceURL
from AtomicString& to AtomicString to work around returning a
reference to a local object. This should not have a measurable
impact on performance.

BUG=279445

Review URL: https://chromiumcodereview.appspot.com/23534033

git-svn-id: svn://svn.chromium.org/blink/trunk@157025 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[SVG] Handle beginEvent for svg animations

Handled beginEvent for svg animations according to http://www.w3.org/TR/SMIL3/smil-timing.html#q135

R=pdr@chromium.org, schenney@chromium.org, dschulze@chromium.org, fmalita@chromium.org
BUG=269642

Review URL: https://chromiumcodereview.appspot.com/22706003

git-svn-id: svn://svn.chromium.org/blink/trunk@157026 bbb929c8-8fbe-4397-9dbb-9b2b20218538