ImageCapture: introduce image_capture Blob to allow move-only semantics

third_party/WebKit/Source/modules/imagecapture/PhotoCapabilities.idl

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://w3c.github.io/mediacapture-image/index.html#idl-def-PhotoCapabilities
 
 enum FocusMode {
     "unavailable",
     "auto",
     "manual"
 };
 
 [
     RuntimeEnabled=ImageCapture,
 ] interface PhotoCapabilities {
-    // TODO(mcasas): Update the Spec where these members are not readonly.
-    // https://github.com/w3c/mediacapture-image/issues/29
-
     readonly attribute MediaSettingsRange iso;
     // TODO(mcasas): Replace these two with supported and current resolutions.
     // https://github.com/w3c/mediacapture-image/issues/30
     readonly attribute MediaSettingsRange imageHeight;
     readonly attribute MediaSettingsRange imageWidth;
     readonly attribute MediaSettingsRange zoom;
     readonly attribute FocusMode focusMode;
     // TODO(mcasas): Implement all other PhotoCapabilities fields
     // https://crbug.com/518807
 };