Bug 1514640 - Use the vsync id of the skipped composite when we do a catch-up composite. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D15019

--HG--
extra : moz-landing-system : lando

gfx/layers/wr/WebRenderBridgeParent.cpp

@@ -1702,7 +1702,7 @@ bool WebRenderBridgeParent::SampleAnimations(
 void WebRenderBridgeParent::CompositeIfNeeded() {
   if (mSkippedComposite) {
     mSkippedComposite = false;
-    CompositeToTarget(VsyncId(), nullptr, nullptr);
+    CompositeToTarget(mSkippedCompositeId, nullptr, nullptr);
   }
 }
 
@@ -1726,7 +1726,13 @@ void WebRenderBridgeParent::CompositeToTarget(VsyncId aId,
   if (mSkippedComposite ||
       wr::RenderThread::Get()->TooManyPendingFrames(mApi->GetId())) {
     // Render thread is busy, try next time.
-    mSkippedComposite = true;
+    if (!mSkippedComposite) {
+      // Only record the vsync id for the first skipped composite,
+      // since this matches what we do for compressing messages
+      // in CompositorVsyncScheduler::PostCompositeTask.
+      mSkippedComposite = true;
+      mSkippedCompositeId = aId;
+    }
     mPreviousFrameTimeStamp = TimeStamp();
 
     // Record that we skipped presenting a frame for

gfx/layers/wr/WebRenderBridgeParent.h

@@ -392,6 +392,8 @@ class WebRenderBridgeParent final : public PWebRenderBridgeParent,
   wr::Epoch mWrEpoch;
   wr::IdNamespace mIdNamespace;
 
+  VsyncId mSkippedCompositeId;
+
   bool mPaused;
   bool mDestroyed;
   bool mReceivedDisplayList;