Reland of ServiceWorker: Implement StartWorker by using mojo

content/public/app/mojo/content_renderer_manifest.json

 {
   "manifest_version":  1,
   "name": "exe:content_renderer",
   "display_name": "Content Renderer",
   "capabilities": {
     "provided": {
       "all_interfaces": [ "*" ],
       "browser": [
+        "content::mojom::EmbeddedWorkerInstanceClient",
         "content::mojom::EmbeddedWorkerSetup",
         "content::mojom::FrameFactory",
         "content::mojom::TestMojoService",
         "IPC::mojom::ChannelBootstrap",
         "mojom::ResourceUsageReporter",
         "web_cache::mojom::WebCache"
       ]
     },
     "required": {
       // Remove this once http://crbug.com/632818 is fixed.
       "exe:content_browser": {
         "classes":  [ "web" ]
       },
       "mojo:ui": {
         "interfaces": [
           "ui::mojom::Gpu",
           "ui::mojom::GpuService"
         ]
       }
     }
   }
 }