[FastTextAutosizer] Rework form input handling

This patch reworks how we handle form input by removing the hash
lookup of specific element types in favor of checking
isFormControlElement. This is faster and includes the fieldset
element which is considered a form control, fixing a bug on
http://forum.nationstates.net.

Detailed description of changes:
1) Switch isFormInput's argument from const Element* to
const RenderObject* which lets us move the duplicated
node logic from the callers into isFormInput. One of the
callers used node() and the other used generatingNode()
so this may have fixed a subtle bug as well.
2) Change isFormInput to check isFormControlElement
instead of checking the tagname.
3) Add a special-case for HTMLTextAreaElement which
should be autosized unlike the other form control
elements. See various special-cases sprinkled in
FastTextAutosizer.cpp
4) Rename isFormInput to isNonTextAreaFormControl.
5) Refactor blockContainsFormInput as
blockOrImmediateChildrenAreFormControls and cleanup
the code.

BUG=373539

Review URL: https://codereview.chromium.org/295913002

git-svn-id: svn://svn.chromium.org/blink/trunk@174437 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Try waiting for image load in flaky svg test

It's not clear to me why these tests are flaking, but one possibility is
that there's a race with the image loading and layout.  This is a test
to wait for the repaint test until the image has loaded.

R=pdr@chromium.org
BUG=374936

Review URL: https://codereview.chromium.org/292983008

git-svn-id: svn://svn.chromium.org/blink/trunk@174438 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make ChildNodeInsertionNotifier::notify iterative for detached subtrees

There's no reason for all this recursion, we can just use NodeTraversal
instead.

Review URL: https://codereview.chromium.org/291273002

git-svn-id: svn://svn.chromium.org/blink/trunk@174439 bbb929c8-8fbe-4397-9dbb-9b2b20218538