refactor(Compiler): improve the error message on component load error

by adding the fetched url.

relates to #1460

modules/angular2/test/render/dom/compiler/compiler_common_tests.ts

@@ -103,7 +103,8 @@ export function runCompilerCommonTests() {
            PromiseWrapper.catchError(
                compiler.compile(new ViewDefinition({componentId: 'someId', absUrl: 'someUrl'})),
                (e) => {
-                 expect(e.message).toContain(`Failed to load the template "someId"`);
+                 expect(e.message).toEqual(
+                     'Failed to load the template for "someId" : Failed to fetch url "someUrl"');
                  async.done();
                  return null;
                });
@@ -208,9 +209,9 @@ class FakeTemplateLoader extends TemplateLoader {
 
     if (isPresent(template.absUrl)) {
       var content = MapWrapper.get(this._urlData, template.absUrl);
-      if (isPresent(content)) {
-        return PromiseWrapper.resolve(DOM.createTemplate(content));
-      }
+      return isPresent(content) ?
+                 PromiseWrapper.resolve(DOM.createTemplate(content)) :
+                 PromiseWrapper.reject(`Failed to fetch url "${template.absUrl}"`, null);
     }
 
     return PromiseWrapper.reject('Load failed', null);

modules/angular2/test/render/dom/compiler/template_loader_spec.ts

@@ -78,7 +78,7 @@ export function main() {
          var template = new ViewDefinition({absUrl: 'base/foo'});
          PromiseWrapper.then(loader.load(template), function(_) { throw 'Unexpected response'; },
                              function(error) {
-                               expect(error).toEqual('Failed to load base/foo');
+                               expect(error.message).toEqual('Failed to fetch url "base/foo"');
                                async.done();
                              });
          xhr.flush();