Support CanvasPattern.setTransform

Patterns have a transformation matrix, which controls how the pattern is used when it is painted. 

Initially, a pattern's transformation matrix must be the identity transform. 

When the setTransform() method is invoked on the pattern, the user agent must replace the pattern's
transformation matrix with the one described by the SVGMatrix object provided as an argument to the method.

Specification: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-canvaspattern-settransform
IDL Definition: http://www.whatwg.org/specs/web-apps/current-work/multipage/scripting.html#2dcontext:dom-canvaspattern-settransform
Intent to Implement: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/dUt2_2xn3NU

BUG=289572
R=junov@chromium.org

Review URL: https://codereview.chromium.org/527193002

git-svn-id: svn://svn.chromium.org/blink/trunk@181737 bbb929c8-8fbe-4397-9dbb-9b2b20218538
In generated dictionary toImpl(), throw all exceptions via ExceptionState

This allows us to simplify callers by not having a v8::TryCatch there, and
instead only check the ExceptionState object.

Review URL: https://codereview.chromium.org/556273003

git-svn-id: svn://svn.chromium.org/blink/trunk@181738 bbb929c8-8fbe-4397-9dbb-9b2b20218538