fix(ngBind): use same json conversion logic as $interpolate

Fixes #11716

BREAKING CHANGE:

`ngBind` now uses the same logic as $interpolate (i.e. {{myString}}) when
binding, which means objects are now transformed to string either with an
object's custom toString() function, or if the object doesn't have one, with JSON.stringify.
Previously, ngBind would use always use toString().

The following examples show the different output:
```js
$scope.myPlainObject = {a: 1, b: 2};
$scope.myCustomObject = {a: 1, b: 2, toString: function() {return 'a+b';}};
```

Plain Object:
```html
<!-- Before: -->
<span ng-bind="myPlainObject">[object Object]</span>

<!-- After: -->
<span ng-bind="myPlainObject">{"a":1,"b":2}</span>
```

Object with custom toString():

```html
<!-- Before: -->
<span ng-bind="myCustomObject">[object Object]</span>

<!-- After: -->
<span ng-bind="myCustomObject">a+b</span>
```

Migration:
If you want the output of `toString()`, use a custom filter:
```js
angular.module('myApp').filter('toString', function() {
  return function toString(value) {
    return value.toString();
  };
});
```

```html
<span ng-bind="myObject | toString">[object Object]</span>
```

Author: Narretz

src/.jshintrc

@@ -96,6 +96,7 @@
     "createMap": false,
     "VALIDITY_STATE_PROPERTY": false,
     "reloadWithDebugInfo": false,
+    "stringify": false,
 
     "NODE_TYPE_ELEMENT": false,
     "NODE_TYPE_ATTRIBUTE": false,

src/Angular.js

@@ -87,6 +87,7 @@
   getBlockNodes: true,
   hasOwnProperty: true,
   createMap: true,
+  stringify: true,
 
   NODE_TYPE_ELEMENT: true,
   NODE_TYPE_ATTRIBUTE: true,
@@ -1929,6 +1930,28 @@ function createMap() {
   return Object.create(null);
 }
 
+
+function stringify(value) {
+  if (value == null) { // null || undefined
+    return '';
+  }
+  switch (typeof value) {
+    case 'string':
+      break;
+    case 'number':
+      value = '' + value;
+      break;
+    default:
+      if (isFunction(value.toString) && value.toString !== Object.prototype.toString && !isArray(value)) {
+        value = value.toString();
+      } else {
+        value = toJson(value);
+      }
+  }
+
+  return value;
+}
+
 var NODE_TYPE_ELEMENT = 1;
 var NODE_TYPE_ATTRIBUTE = 2;
 var NODE_TYPE_TEXT = 3;

src/ng/directive/ngBind.js

@@ -60,7 +60,7 @@ var ngBindDirective = ['$compile', function($compile) {
         $compile.$$addBindingInfo(element, attr.ngBind);
         element = element[0];
         scope.$watch(attr.ngBind, function ngBindWatchAction(value) {
-          element.textContent = isUndefined(value) ? '' : value;
+          element.textContent = isUndefined(value) ? '' : stringify(value);
         });
       };
     }

src/ng/interpolate.js

@@ -111,27 +111,6 @@ function $InterpolateProvider() {
         replace(escapedEndRegexp, endSymbol);
     }
 
-    function stringify(value) {
-      if (value == null) { // null || undefined
-        return '';
-      }
-      switch (typeof value) {
-        case 'string':
-          break;
-        case 'number':
-          value = '' + value;
-          break;
-        default:
-          if (isFunction(value.toString) && value.toString !== Object.prototype.toString && !isArray(value)) {
-            value = value.toString();
-          } else {
-            value = toJson(value);
-          }
-      }
-
-      return value;
-    }
-
     //TODO: this is the same as the constantWatchDelegate in parse.js
     function constantWatchDelegate(scope, listener, objectEquality, constantInterp) {
       var unwatch;

test/ng/directive/ngBindSpec.js

@@ -46,6 +46,15 @@ describe('ngBind*', function() {
       expect(element.text()).toEqual('-0false');
     }));
 
+    they('should jsonify $prop', [[{a: 1}, '{"a":1}'], [true, 'true'], [false, 'false']], function(prop) {
+      inject(function($rootScope, $compile) {
+        $rootScope.bind = prop[0];
+        element = $compile('<div ng-bind="bind"></div>')($rootScope);
+        $rootScope.$digest();
+        expect(element.text()).toEqual(prop[1]);
+      });
+    });
+
     it('should one-time bind if the expression starts with two colons', inject(function($rootScope, $compile) {
       element = $compile('<div ng-bind="::a"></div>')($rootScope);
       $rootScope.a = 'lucas';