Fix for input/datalist failure when datalist is created outside document

This patch fixes the failure, where datalist, when created in a shadowroot
outside the document, doesnot behave as expected. This patch changes
HTMLInputElement::resetListAttributeTargetObserver to  update the list
reference when it resets the observer.

TEST=fast/forms/datalist/datalist-inside-shadow-dom.html
BUG=391995

Review URL: https://codereview.chromium.org/371413004

git-svn-id: svn://svn.chromium.org/blink/trunk@178632 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Negative SVGTransform scale values should be correctly stringified

Before this CL, |SVGTransform::valueAsString()| used |AffineTransform::{x,y}Scale}|, which computed transform scale values by computing norm of projected unit vectors. However, that would always return positive values, even if negative scale values were specified.

This CL changes the implementation to use |a| and |d| values instead.
This is valid, as the scale matrix is guaranteed to be in the below simple form when the transform has type |SVG_TRANSFORM_SCALE|:
|xscale    0   0|
|   0   yscale 0|

BUG=393917

Review URL: https://codereview.chromium.org/410573002

git-svn-id: svn://svn.chromium.org/blink/trunk@178633 bbb929c8-8fbe-4397-9dbb-9b2b20218538