fix(dart/transform): Don't set ReflectionCapabilities over an async gap

Update the transformer's `TemplateCompiler` phase to avoid setting
`reflector.reflectionCapabilities`, allowing asynchronous
operations, and restoring the original value, which allows
`reflector.reflectionCapabilities` to get into a bad state.

modules/angular2/test/transform/template_compiler/all_tests.dart

@@ -103,7 +103,6 @@ void allTests() {
       output = await process(new AssetId('a', inputPath));
       _formatThenExpectEquals(output, expected);
     });
-
   });
 }