feat(compiler): assert that Component.style is an array

Part of #7481 (effort to improve error messages)

Closes #7559

modules/angular2/test/compiler/runtime_metadata_fixture.dart

@@ -0,0 +1,9 @@
+library angular2.test.compiler.runtime_metadata_fixture;
+
+import "package:angular2/core.dart" show Component;
+
+// This component is not actually malformed; this fixture is here to
+// make Dart not complain about a missing import for a test case that only
+// matters in an JavaScript app.
+@Component(template: "")
+class MalformedStylesComponent {}

modules/angular2/test/compiler/runtime_metadata_fixture.ts

@@ -0,0 +1,5 @@
+import {Component} from 'angular2/core';
+
+@Component({styles:<any>('foo'), template: ''})
+export class MalformedStylesComponent {
+}

modules/angular2/test/compiler/runtime_metadata_spec.ts

@@ -37,6 +37,7 @@ import {TEST_PROVIDERS} from './test_bindings';
 import {MODULE_SUFFIX} from 'angular2/src/compiler/util';
 import {IS_DART} from 'angular2/src/facade/lang';
 import {PLATFORM_DIRECTIVES} from 'angular2/src/core/platform_directives_and_pipes';
+import {MalformedStylesComponent} from './runtime_metadata_fixture';
 
 export function main() {
   describe('RuntimeMetadataResolver', () => {
@@ -74,6 +75,14 @@ export function main() {
            var expectedEndValue = IS_DART ? 'test/compiler/runtime_metadata_spec.dart' : './';
            expect(value.endsWith(expectedEndValue)).toBe(true);
          }));
+
+      it('should throw when metadata is incorrectly typed',
+         inject([RuntimeMetadataResolver], (resolver: RuntimeMetadataResolver) => {
+           if (!IS_DART) {
+             expect(() => resolver.getDirectiveMetadata(MalformedStylesComponent))
+                 .toThrowError(`Expected 'styles' to be an array of strings.`);
+           }
+         }));
     });
 
     describe('getViewDirectivesMetadata', () => {