Expose VSync pausing through WindowAndroid and pause VSync during webVR presentation

ui/android/java/src/org/chromium/ui/base/WindowAndroid.java

Index: ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
diff --git a/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java b/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
index 882bb14deb693a3976aa16587107f750d30b6bf5..e281ef2d42141e6b52b8286c2abf84b7e7130dcf 100644
--- a/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
+++ b/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
@@ -109,6 +109,9 @@ public class WindowAndroid {
 
     private AndroidPermissionDelegate mPermissionDelegate;
 
+    private boolean mPendingVSyncRequest;

[boliu, 2017/03/15 22:08:11]

hmm.. reading over this, I think it makes more sense to have all this logic in
native in BFS? java can just purely pass through for the set paused call.

[mthiesse, 2017/03/16 00:03:07]

So it couldn't only live in BFS, or WindowAndroid::OnVSync will keep requesting
VSync updates and black-holing them (which I guess wouldn't break anything, but
would be conceptually strange). We would have to make native WindowAndroid and
WindowAndroid::WindowBeginFrameSource both aware of the paused state.

Because of this I have a mild preference for leaving as is. Feel free to insist
though.

[boliu, 2017/03/16 00:45:44]

Actually, I see another issue with moving to native. Some of this code runs
before native library is loaded, and native may not be ready when paused. OK,
add a comment that's why the state is here.

Otherwise, I'd ask this to be moved to native like you suggest.

[mthiesse, 2017/03/16 15:36:05]

Done.

+    private boolean mVSyncPaused;
+
     /**
      * An interface to notify listeners of changes in the soft keyboard's visibility.
      */
@@ -134,6 +137,10 @@ public class WindowAndroid {
     private final VSyncMonitor.Listener mVSyncListener = new VSyncMonitor.Listener() {
         @Override
         public void onVSync(VSyncMonitor monitor, long vsyncTimeMicros) {
+            if (mVSyncPaused) {
+                mPendingVSyncRequest = true;
+                return;
+            }
             if (mNativeWindowAndroid != 0) {
                 nativeOnVSync(mNativeWindowAndroid,
                               vsyncTimeMicros,
@@ -496,7 +503,11 @@ public class WindowAndroid {
     }
 
     @CalledByNative
-    private void requestVSyncUpdate() {
+    protected void requestVSyncUpdate() {

[boliu, 2017/03/15 22:08:11]

keep private

[mthiesse, 2017/03/16 00:03:07]

Done.

+        if (mVSyncPaused) {
+            mPendingVSyncRequest = true;
+            return;
+        }
         mVSyncMonitor.requestUpdate();
     }
 
@@ -557,6 +568,7 @@ public class WindowAndroid {
     public long getNativePointer() {
         if (mNativeWindowAndroid == 0) {
             mNativeWindowAndroid = nativeInit(mDisplayAndroid.getDisplayId());
+            if (mVSyncPaused) nativeSetVSyncPaused(mNativeWindowAndroid, true);

[boliu, 2017/03/15 22:08:11]

hmm, this doesn't look correct to me, why is vsync initially paused? what's
unpausing it then?

[mthiesse, 2017/03/16 00:03:07]

Well, whatever paused it is responsible for unpausing it, it's not initially
paused. If something wants to pause the vsync loop before the native
WindowAndroid is initialized I don't see why not.

[boliu, 2017/03/16 00:45:44]

Oh so the assumption is that native start out as unpaused? Why not not assume
that and just pass paused here unconditionally?

[mthiesse, 2017/03/16 15:36:06]

Done.

         }
         return mNativeWindowAndroid;
     }
@@ -724,6 +736,16 @@ public class WindowAndroid {
         }
     }
 
+    /**
+     * Pauses/Unpauses the VSync loop. A paused VSync loop will stop the compositor for this window,

[boliu, 2017/03/15 22:08:11]

nit: it's not a loop (in my head at least).. so drop the "loop" part

[mthiesse, 2017/03/16 00:03:07]

Done.

+     * preventing requestAnimationFrame callbacks from firing, etc.
+     */
+    public void setVSyncPaused(boolean paused) {
+        mVSyncPaused = paused;

[boliu, 2017/03/15 22:08:11]

generally, these things have an early out when mVSyncPaused and paused are equal

[mthiesse, 2017/03/16 00:03:07]

Done.

+        if (!mVSyncPaused && mPendingVSyncRequest) requestVSyncUpdate();
+        if (mNativeWindowAndroid != 0) nativeSetVSyncPaused(mNativeWindowAndroid, paused);
+    }
+
     private native long nativeInit(int displayId);
     private native void nativeOnVSync(long nativeWindowAndroid,
                                       long vsyncTimeMicros,
@@ -731,6 +753,7 @@ public class WindowAndroid {
     private native void nativeOnVisibilityChanged(long nativeWindowAndroid, boolean visible);
     private native void nativeOnActivityStopped(long nativeWindowAndroid);
     private native void nativeOnActivityStarted(long nativeWindowAndroid);
+    private native void nativeSetVSyncPaused(long nativeWindowAndroid, boolean paused);
     private native void nativeDestroy(long nativeWindowAndroid);
 
 }