feat(dart/transform): Use angular2/platform/browser as bootstrap lib

Update the Angular 2 transformer to recognize
`package:angular2/platform/browser.dart` as the library which exports
the `bootstrap` function.

Update playground, examples, benchmarks, & tests to import bootstrap from
platform/browser.

Closes #7647

modules/angular2/examples/compiler/ts/url_resolver/url_resolver.ts

@@ -1,5 +1,5 @@
 import {provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {UrlResolver} from 'angular2/compiler';
 
 var MyApp: any;

modules/angular2/examples/core/forms/ts/ng_validators/ng_validators.ts

@@ -1,4 +1,4 @@
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {NG_VALIDATORS} from 'angular2/common';
 import {Provider} from 'angular2/core';
 

modules/angular2/examples/core/pipes/ts/async_pipe/async_pipe_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {Observable, Subscriber} from 'rxjs/Rx';
 
 // #docregion AsyncPipe

modules/angular2/examples/core/pipes/ts/date_pipe/date_pipe_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 
 // #docregion DatePipe
 @Component({

modules/angular2/examples/core/pipes/ts/json_pipe/json_pipe_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 
 // #docregion JsonPipe
 @Component({

modules/angular2/examples/core/pipes/ts/lowerupper_pipe/lowerupper_pipe_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 
 // #docregion LowerUpperPipe
 @Component({

modules/angular2/examples/core/pipes/ts/number_pipe/number_pipe_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 
 // #docregion NumberPipe
 @Component({

modules/angular2/examples/core/pipes/ts/slice_pipe/slice_pipe_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 
 // #docregion SlicePipe_string
 @Component({

modules/angular2/examples/core/ts/prod_mode/prod_mode_example.ts

@@ -1,6 +1,6 @@
 // #docregion enableProdMode
 import {enableProdMode} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {MyComponent} from './my_component';
 
 enableProdMode();

modules/angular2/examples/router/ts/can_activate/can_activate_example.ts

@@ -1,5 +1,5 @@
 import {provide, Component} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {
   CanActivate,
   RouteConfig,

modules/angular2/examples/router/ts/can_deactivate/can_deactivate_example.ts

@@ -1,5 +1,5 @@
 import {provide, Component} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {
   CanDeactivate,
   RouteConfig,

modules/angular2/examples/router/ts/on_activate/on_activate_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {
   OnActivate,
   ComponentInstruction,

modules/angular2/examples/router/ts/on_deactivate/on_deactivate_example.ts

@@ -1,5 +1,5 @@
 import {Component, Injectable, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {
   OnDeactivate,
   ComponentInstruction,

modules/angular2/examples/router/ts/reuse/reuse_example.ts

@@ -1,5 +1,5 @@
 import {Component, provide} from 'angular2/core';
-import {bootstrap} from 'angular2/bootstrap';
+import {bootstrap} from 'angular2/platform/browser';
 import {
   CanActivate,
   RouteConfig,