fix(css_shim): fixes multiple uses of polyfill-unscoped-rule.

Author: rkirov

modules/angular2/src/render/dom/shadow_dom/shadow_css.ts

@@ -258,7 +258,7 @@ export class ShadowCss {
       var rule = m[0];
       rule = StringWrapper.replace(rule, m[2], '');
       rule = StringWrapper.replace(rule, m[1], m[3]);
-      r = rule + '\n\n';
+      r += rule + '\n\n';
     }
     return r;
   }

modules/angular2/test/render/dom/shadow_dom/shadow_css_spec.ts

@@ -123,6 +123,14 @@ export function main() {
       expect(StringWrapper.contains(css, '#menu > .bar {;color:blue;}')).toBeTruthy();
     });
 
+    it('should support multiple instances polyfill-unscoped-rule', () => {
+      var css = s("polyfill-unscoped-rule {content: 'foo';color: blue;}" +
+                      "polyfill-unscoped-rule {content: 'bar';color: blue;}",
+                  'a');
+      expect(StringWrapper.contains(css, 'foo {;color:blue;}')).toBeTruthy();
+      expect(StringWrapper.contains(css, 'bar {;color:blue;}')).toBeTruthy();
+    });
+
     it('should support polyfill-rule', () => {
       var css = s("polyfill-rule {content: ':host.foo .bar';color: blue;}", 'a', 'a-host');
       expect(css).toEqual('[a-host].foo .bar {color:blue;}');