Fix for link highlighting of <img> links

Temporary fix for <img> inside <a>. I changed the node that gets passed to the LinkHighlight object. Previously, when a node was tapped, we'd go up the tree until we find a node that causes a "hand cursor" and use that. Now, we do the same but we stop ascending up the tree if a node isn't contained by its parent's box.

In the long term, the LinkHighlight should be changed to use the entire hit testing region of the node, rather than the line box.

Note: This is relanding of https://codereview.chromium.org/24307004/. The only change from that patch is in WebViewImpl.cpp
BUG=170673

Review URL: https://chromiumcodereview.appspot.com/24376003

git-svn-id: svn://svn.chromium.org/blink/trunk@158232 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Expose ImageDecoder::decodedSize for DeferredImageDecoder

Added ImageDecoder::decodedSize to return the decoded size which is
normally the actuall image size but may be smaller because of
maxDecodedSize. DeferredImageDecoder uses it as a part of key
(scaledSize) in the decoding store to store and find a specific
decoder.

BUG=276666
TEST=DeferredImageDecoder.decodedSize and updated JPEGImageDecoderTest.*.

Review URL: https://chromiumcodereview.appspot.com/23551014

git-svn-id: svn://svn.chromium.org/blink/trunk@158233 bbb929c8-8fbe-4397-9dbb-9b2b20218538