Fill in some canvas doc blanks.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "AbstractWorker": {
       "members": {
         "errorEvent": [
           "/**",
           "   * Static factory designed to expose `error` events to event",
           "   * handlers that are not necessarily instances of [AbstractWorker].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
@@ skipping 181 matching lines @@
         " * This context is extended by [CanvasRenderingContext2D] and",
         " * [WebGLRenderingContext].",
         " */"
       ],
       "members": {
         "canvas": [
           "/// Reference to the canvas element to which this context belongs."
         ]
       }
     },
+    "CanvasRenderingContext2D": {
+      "members": {
+        "currentPath": [
+          "/**",
+          "   * The current default path of this canvas context, if there is one.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Current default path]",
+          "   * (http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#current-default-path)",
+          "   * from WHATWG.",
+          "   */"
+        ],
+        "imageSmoothingEnabled": [
+          "/**",
+          "   * Whether images and patterns on this canvas will be smoothed when this",
+          "   * canvas is scaled.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [Image smoothing]",
+          "   * (http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#image-smoothing)",
+          "   * from WHATWG.",
+          "   */"
+        ],
+        "webkitBackingStorePixelRatio": [
+          "/**",
+          "   * The ratio between this canvas' backing store dimensions and the canvas'",
+          "   * logical dimensions.",
+          "   *",
+          "   * ## Other resources",
+          "   *",
+          "   * * [High DPI Canvas tutorial]",
+          "   * (http://www.html5rocks.com/en/tutorials/canvas/hidpi/) from HTML5Rocks.",
+          "   */"
+        ]
+      }
+    },
     "Clipboard": {
       "members": {
         "getData": [
           "/**",
           "   * Gets the data for the specified type.",
           "   *",
           "   * The data is only available from within a drop operation (such as an",
           "   * [Element.onDrop] event) and will return `null` before the event is",
           "   * triggered.",
           "   *",
@@ skipping 4373 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }