Allow CompoundObserver to report changes in value from added to open

R=arv
BUG=

Review URL: https://codereview.appspot.com/88160051

Author: rafaelw

src/observe.js

@@ -875,9 +875,10 @@
     }
   });
 
-  function CompoundObserver() {
+  function CompoundObserver(reportChangesOnOpen) {
     Observer.call(this);
 
+    this.reportChangesOnOpen_ = reportChangesOnOpen;
     this.value_ = [];
     this.directObserver_ = undefined;
     this.observed_ = [];
@@ -889,23 +890,22 @@
     __proto__: Observer.prototype,
 
     connect_: function() {
-      this.check_(undefined, true);
-
-      if (!hasObserve)
-        return;
-
-      var object;
-      var needsDirectObserver = false;
-      for (var i = 0; i < this.observed_.length; i += 2) {
-        object = this.observed_[i]
-        if (object !== observerSentinel) {
-          needsDirectObserver = true;
-          break;
+      if (hasObserve) {
+        var object;
+        var needsDirectObserver = false;
+        for (var i = 0; i < this.observed_.length; i += 2) {
+          object = this.observed_[i]
+          if (object !== observerSentinel) {
+            needsDirectObserver = true;
+            break;
+          }
         }
+
+        if (needsDirectObserver)
+          this.directObserver_ = getObservedSet(this, object);
       }
 
-      if (needsDirectObserver)
-        this.directObserver_ = getObservedSet(this, object);
+      this.check_(undefined, !this.reportChangesOnOpen_);
     },
 
     disconnect_: function() {
@@ -926,14 +926,23 @@
       if (this.state_ != UNOPENED && this.state_ != RESETTING)
         throw Error('Cannot add paths once started.');
 
-      this.observed_.push(object, getPath(path));
+      var path = getPath(path);
+      this.observed_.push(object, path);
+      if (!this.reportChangesOnOpen_)
+        return;
+      var index = this.observed_.length / 2 - 1;
+      this.value_[index] = path.getValueFrom(object);
     },
 
     addObserver: function(observer) {
       if (this.state_ != UNOPENED && this.state_ != RESETTING)
         throw Error('Cannot add observers once started.');
 
       this.observed_.push(observerSentinel, observer);
+      if (!this.reportChangesOnOpen_)
+        return;
+      var index = this.observed_.length / 2 - 1;
+      this.value_[index] = observer.open(this.deliver, this);
     },
 
     startReset: function() {

tests/test.js

@@ -72,8 +72,9 @@ function assertPathChanges(expectNewValue, expectOldValue, dontDeliver) {
 }
 
 function assertCompoundPathChanges(expectNewValues, expectOldValues,
-                                   expectObserved) {
-  observer.deliver();
+                                   expectObserved, dontDeliver) {
+  if (!dontDeliver)
+    observer.deliver();
 
   assert.isTrue(callbackInvoked);
 
@@ -84,8 +85,10 @@ function assertCompoundPathChanges(expectNewValues, expectOldValues,
   assert.deepEqual(expectOldValues, oldValues);
   assert.deepEqual(expectObserved, observed);
 
-  assert.isTrue(window.dirtyCheckCycleCount === undefined ||
-                window.dirtyCheckCycleCount === 1);
+  if (!dontDeliver) {
+    assert.isTrue(window.dirtyCheckCycleCount === undefined ||
+                  window.dirtyCheckCycleCount === 1);
+  }
 
   callbackArgs = undefined;
   callbackInvoked = false;
@@ -1066,6 +1069,7 @@ suite('CompoundObserver Tests', function() {
     observer.addPath(model, 'b');
     observer.addPath(model, Path.get('c'));
     observer.open(callback);
+    assertNoChanges();
 
     var observerCallbackArg = [model, Path.get('a'),
                                model, Path.get('b'),
@@ -1102,6 +1106,25 @@ suite('CompoundObserver Tests', function() {
     observer.close();
   });
 
+  test('reportChangesOnOpen', function() {
+    var model = { a: 1, b: 2, c: 3 };
+
+    observer = new CompoundObserver(true);
+    observer.addPath(model, 'a');
+    observer.addPath(model, 'b');
+    observer.addPath(model, Path.get('c'));
+
+    model.a = -10;
+    model.b = 20;
+    observer.open(callback);
+    var observerCallbackArg = [model, Path.get('a'),
+                               model, Path.get('b'),
+                               model, Path.get('c')];
+    assertCompoundPathChanges([-10, 20, 3], [1, 2, ],
+                              observerCallbackArg, true);
+    observer.close();
+  });
+
   test('All Observers', function() {
     function ident(value) { return value; }