html_viewer: Move webcrypto to a place where html_viewer can use it.

mojo/services/html_viewer/blink_platform_impl.cc

Index: mojo/services/html_viewer/blink_platform_impl.cc
diff --git a/mojo/services/html_viewer/blink_platform_impl.cc b/mojo/services/html_viewer/blink_platform_impl.cc
index 71b024aaedf63c41b341496d4484c9ecfe876587..e9975a99cad1e4cd1f3ddcaa197132e6e3cf837e 100644
--- a/mojo/services/html_viewer/blink_platform_impl.cc
+++ b/mojo/services/html_viewer/blink_platform_impl.cc
@@ -269,6 +269,10 @@ blink::WebGestureCurve* BlinkPlatformImpl::createFlingAnimationCurve(
              is_main_thread).release();
 }
 
+blink::WebCrypto* BlinkPlatformImpl::crypto() {
+  return &web_crypto_;
+}
+
 blink::WebNotificationManager*
 BlinkPlatformImpl::notificationManager() {
   return &web_notification_manager_;