Exposing DOM float & double types as double rather than num.

tools/dom/templates/html/impl/impl_CanvasRenderingContext2D.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 
   /**
@@ skipping 77 matching lines @@
    * from [source].
    *   * [drawImage](http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-drawimage)
    * from the WHATWG.
    */
   @DomName('CanvasRenderingContext2D.drawImage')
   void drawImageToRect(CanvasImageSource source, Rect destRect,
       {Rect sourceRect}) {
 $if DART2JS
     if (sourceRect == null) {
       drawImageScaled(source,
-          destRect.left,
-          destRect.top,
-          destRect.width,
-          destRect.height);
+          destRect.left.toDouble(),
+          destRect.top.toDouble(),
+          destRect.width.toDouble(),
+          destRect.height.toDouble());
     } else {
       drawImageScaledFromSource(source,
-          sourceRect.left,
-          sourceRect.top,
-          sourceRect.width,
-          sourceRect.height,
-          destRect.left,
-          destRect.top,
-          destRect.width,
-          destRect.height);
+          sourceRect.left.toDouble(),
+          sourceRect.top.toDouble(),
+          sourceRect.width.toDouble(),
+          sourceRect.height.toDouble(),
+          destRect.left.toDouble(),
+          destRect.top.toDouble(),
+          destRect.width.toDouble(),
+          destRect.height.toDouble());
     }
 $else
     if (sourceRect == null) {
       _drawImage(source,
-          destRect.left,
-          destRect.top,
-          destRect.width,
-          destRect.height);
+          destRect.left.toDouble(),
+          destRect.top.toDouble(),
+          destRect.width.toDouble(),
+          destRect.height.toDouble());
     } else {
       _drawImage(source,
-          sourceRect.left,
-          sourceRect.top,
-          sourceRect.width,
-          sourceRect.height,
-          destRect.left,
-          destRect.top,
-          destRect.width,
-          destRect.height);
+          sourceRect.left.toDouble(),
+          sourceRect.top.toDouble(),
+          sourceRect.width.toDouble(),
+          sourceRect.height.toDouble(),
+          destRect.left.toDouble(),
+          destRect.top.toDouble(),
+          destRect.width.toDouble(),
+          destRect.height.toDouble());
     }
 $endif
   }
 
   /**
    * Draws an image from a CanvasImageSource to this canvas.
    *
    * The entire image from [source] will be drawn to this context with its top
    * left corner at the point ([destX], [destY]). If the image is
    * larger than canvas will allow, the image will be clipped to fit the
@@ skipping 120 matching lines @@
   @DomName('CanvasRenderingContext2D.lineDashOffset')
   void set lineDashOffset(num value) => JS('void',
       'typeof #.lineDashOffset != "undefined" ? #.lineDashOffset = # : '
       '#.webkitLineDashOffset = #', this, this, value, this, value);
 $else
   // TODO(amouravski): Add Dartium native methods for drawImage once we figure
   // out how to not break native bindings.
 $endif
 }