Changed VRLayer's left/rightBounds to match the spec

third_party/WebKit/Source/modules/vr/VRLayer.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.
 
 typedef HTMLCanvasElement VRSource;
 
 // http://mozvr.github.io/webvr-spec/webvr.html#vrlayer
 [
     RuntimeEnabled=WebVR
 ] dictionary VRLayer {
   // The canvas to be presented to the VRDisplay
   VRSource? source = null;
 
   // The left and right bounds contain 4 git statvalues defining the texture bounds
   // within the canvas to present to the eye in UV space.
   // [0] left offset of the bounds (0.0 - 1.0)
   // [1] top offset of the bounds (0.0 - 1.0)
   // [2] width of the bounds (0.0 - 1.0)
   // [3] height of the bounds (0.0 - 1.0)
-  sequence<float>? leftBounds; //= [0.0, 0.0, 0.5, 1.0];
-  sequence<float>? rightBounds; //= [0.5, 0.0, 0.5, 1.0];
+  sequence<float> leftBounds = []; //= [0.0, 0.0, 0.5, 1.0];
+  sequence<float> rightBounds = []; //= [0.5, 0.0, 0.5, 1.0];
 };