make path public on PathObserver and change third argument from path to the PathObserver instance

[email protected], jmesserly
BUG=

Review URL: https://codereview.appspot.com/99660045

Author: rafaelw

src/observe.js

@@ -1004,6 +1004,10 @@
   PathObserver.prototype = createObject({
     __proto__: Observer.prototype,
 
+    get path() {
+      return this.path_;
+    },
+
     connect_: function() {
       if (hasObserve)
         this.directObserver_ = getObservedSet(this, this.object_);
@@ -1030,7 +1034,7 @@
       if (skipChanges || areSameValue(this.value_, oldValue))
         return false;
 
-      this.report_([this.value_, oldValue, this.path_]);
+      this.report_([this.value_, oldValue, this]);
       return true;
     },
 

tests/test.js

@@ -469,7 +469,8 @@ suite('PathObserver Tests', function() {
     assert.strictEqual(args.length, 3);
     assert.strictEqual(args[0], 'baz');
     assert.strictEqual(args[1], 'bar');
-    assert.strictEqual(args[2], path);
+    assert.strictEqual(args[2], observer);
+    assert.strictEqual(args[2].path, path);
     observer.close();
   });