Expose setValue on PathObserver

R=arv
BUG=

Review URL: https://codereview.appspot.com/13393044

src/observe.js

@@ -583,7 +583,8 @@
     }
   };
 
-  function PathObserver(object, pathString, callback, target, token, valueFn) {
+  function PathObserver(object, pathString, callback, target, token, valueFn,
+                        setValueFn) {
     var path = getPath(pathString);
     if (!path) {
       // Invalid path.
@@ -608,6 +609,7 @@
 
     Observer.call(this, object, callback, target, token);
     this.valueFn = valueFn;
+    this.setValueFn = setValueFn;
     this.path = path;
 
     this.connect();
@@ -663,6 +665,14 @@
       }
 
       this.oldValue = this.value;
+    },
+
+    setValue: function(newValue) {
+      if (!this.path)
+        return;
+      if (typeof this.setValueFn === 'function')
+        newValue = this.setValueFn(newValue);
+      this.path.setValueFrom(this.object, newValue);
     }
   });
 

tests/test.js

@@ -209,6 +209,24 @@ suite('PathObserver Tests', function() {
     observer.close();
   });
 
+  test('Path setValue', function() {
+    var arr = {};
+
+    arr.foo = 'bar';
+    observer = new PathObserver(arr, 'foo', callback);
+    arr.foo = 'baz';
+
+    observer.setValue('bat');
+    assert.strictEqual(arr.foo, 'bat');
+    assertPathChanges('bat', 'bar');
+
+    observer.setValue('bot');
+    observer.reset();
+    assertNoChanges();
+
+    observer.close();
+  });
+
   test('Degenerate Values', function() {
     observer = new PathObserver(null, '', callback);
     assert.equal(null, observer.value);