VR: Fix the size of the JS dialog

The size is fixed to follow the design

BUG=808560

Change-Id: If63ebbd676d62acd4cbc46081551d73835ced49c
Reviewed-on: https://chromium-review.googlesource.com/900055Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Amirhossein Simjour <asimjour@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534156}

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrDialog.java

@@ -24,6 +24,8 @@ public class VrDialog extends FrameLayout {
      */
     public VrDialog(Context context, VrDialogManager vrDialogManager) {
         super(context);
+        setLayoutParams(
+                new FrameLayout.LayoutParams(DIALOG_WIDTH, ViewGroup.LayoutParams.WRAP_CONTENT));
         mVrDialogManager = vrDialogManager;
     }