Fix unknown type error in html_*.dart

Fix unknown type error in html_*.dart

The type Matrix is used unqualified in html_*.dart (CanvasRenderingContext2D.currentTransform).  This imports that type only unqualified.

Is there a better way to do this?

R=blois@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31585

[blois, 2014-01-07 22:05:55]

lgtm

Can't think of a better way, alternative would be to edit it by hand to add the
svg. prefix. Auto-generating it that way is non-trivial.

[vsm, 2014-01-07 22:11:01]

Committed patchset #1 manually as r31585 (presubmit successful).