fix(compiler): OneWayOneTime bindings now wait for the model to stablize

lib/core_dom/element_binder.dart

@@ -176,9 +176,18 @@ class ElementBinder {
 
           Expression attrExprFn = _parser(nodeAttrs[attrName]);
           var watch;
+          var lastOneTimeValue;
           watch = scope.watch(nodeAttrs[attrName], (value, _) {
-            if (dstPathFn.assign(controller, value) != null) {
-              watch.remove();
+            if ((lastOneTimeValue = dstPathFn.assign(controller, value)) != null && watch != null) {
+                var watchToRemove = watch;
+                watch = null;
+                scope.rootScope.domWrite(() {
+                  if (lastOneTimeValue != null) {
+                    watchToRemove.remove();
+                  } else {  // It was set to non-null, but stablized to null, wait.
+                    watch = watchToRemove;
+                  }
+                });
             }
           }, formatters: formatters);
           break;

test/core_dom/compiler_spec.dart

@@ -269,7 +269,8 @@ void main() {
           ..bind(SometimesComponent)
           ..bind(ExprAttrComponent)
           ..bind(LogElementComponent)
-          ..bind(SayHelloFormatter);
+          ..bind(SayHelloFormatter)
+          ..bind(OneTimeDecorator);
       });
 
       it('should select on element', async(() {
@@ -690,6 +691,64 @@ void main() {
           }
         }));
       });
+
+      describe('bindings', () {
+        it('should set a one-time binding with the correct value', (Logger logger) {
+          _.compile(r'<div one-time="v"></div>');
+
+          _.rootScope.context['v'] = 1;
+
+          var context = _.rootScope.context;
+          _.rootScope.watch('3+4', (v, _) => context['v'] = v);
+
+          // In the 1st digest iteration:
+          //   v will be set to 7
+          //   OneTimeDecorator.value will be set to 1
+          // In the 2nd digest iteration:
+          //   OneTimeDecorator.value will be set to 7
+          _.rootScope.apply();
+
+          expect(logger).toEqual([1, 7]);
+        });
+
+        it('should keep one-time binding until it is set to non-null', (Logger logger) {
+          _.compile(r'<div one-time="v"></div>');
+          _.rootScope.context['v'] = null;
+          _.rootScope.apply();
+          expect(logger).toEqual([null]);
+
+          _.rootScope.context['v'] = 7;
+          _.rootScope.apply();
+          expect(logger).toEqual([null, 7]);
+
+          // Check that the binding is removed.
+          _.rootScope.context['v'] = 8;
+          _.rootScope.apply();
+          expect(logger).toEqual([null, 7]);
+        });
+
+        it('should remove the one-time binding only if it stablizied to null', (Logger logger) {
+          _.compile(r'<div one-time="v"></div>');
+
+          _.rootScope.context['v'] = 1;
+
+          var context = _.rootScope.context;
+          _.rootScope.watch('3+4', (v, _) => context['v'] = null);
+
+          _.rootScope.apply();
+          expect(logger).toEqual([1, null]);
+
+          // Even though there was a null in the unstable model, we shouldn't remove the binding
+          context['v'] = 8;
+          _.rootScope.apply();
+           expect(logger).toEqual([1, null, 8]);
+
+          // Check that the binding is removed.
+          _.rootScope.context['v'] = 9;
+          _.rootScope.apply();
+          expect(logger).toEqual([1, null, 8]);
+        });
+      });
     });
 
 
@@ -1130,3 +1189,14 @@ class LogElementComponent{
     logger(shadowRoot);
   }
 }
+
+@Decorator(
+    selector: '[one-time]',
+    map: const {
+      'one-time': '=>!value'
+})
+class OneTimeDecorator {
+  Logger log;
+  OneTimeDecorator(this.log);
+  set value(v) => log(v);
+}