Don't dispatch vrdisplayactivate event if the page that listens for it is invisible

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

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrDaydreamApi.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrDaydreamApi.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrDaydreamApi.java
index 8e4169c27bc9edc62032298abe661618bc4bfe8b..1d8976696145ce5871d36eaaa8be04658ae68b7f 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrDaydreamApi.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrDaydreamApi.java
@@ -57,4 +57,9 @@ public interface VrDaydreamApi {
      * @return Whether the current Viewer is a Daydream Viewer.
      */
     Boolean isDaydreamCurrentViewer();
+
+    /**
+     * Launch the stereoscopic, 3D VR launcher homescreen.
+     */
+    void launchVrHomescreen();
 }