Remove 'String::append' from some of the blink source.

Replaced with StringBuilder whereever possible for (marginally) better performance.

BUG=268281

Review URL: https://codereview.chromium.org/124943003

git-svn-id: svn://svn.chromium.org/blink/trunk@164851 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[DevTools] Restrict popover to the main DevTools element.

BUG=331202

Review URL: https://codereview.chromium.org/132043003

git-svn-id: svn://svn.chromium.org/blink/trunk@164852 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Implement Node.lookupPrefix per DOM4.

The spec for this is here:
<http://dom.spec.whatwg.org/#dom-node-lookupprefix>

This simplifies lookupNamespacePrefix, renames it to
locateNamespacePrefix to match the language in the DOM4 spec, and
pushes it down to Element which is the only kind of node for which it
makes sense.

This also removes Node::prefix. Callers that want to know prefixes
should be aware when they're dealing with something with a name (that
is, an element or an attribute.)

BUG=325922

Review URL: https://codereview.chromium.org/126713005

git-svn-id: svn://svn.chromium.org/blink/trunk@164853 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[import] Refactoring: Get rid of HTMLImport::isProcessing()

This change eliminates confusing isProcessing() and
exposes ownsLoader() instead. It clarify the logic in
HTMLImport::isBlockingFollowersFromRunningScript().

BUG=none
TEST=none
R=dglazkov,dominicc

Review URL: https://codereview.chromium.org/131043003

git-svn-id: svn://svn.chromium.org/blink/trunk@164854 bbb929c8-8fbe-4397-9dbb-9b2b20218538