Bug 1503877 - Handle PauseComposition correctly with webrender enabled. r=kats

On android with webrender enabled, minimising the app results in an
assertion failure: CompositorBridgeParent::DidComposite asserts that
it should not be called with a webrender compositor.

This makes it so that that in CompositorBridgeParent::PauseComposition
we call NotifyPipelineRendered instead of DidComposite for webrender
compositors.

Differential Revision: https://phabricator.services.mozilla.com/D10563

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

gfx/layers/ipc/CompositorBridgeParent.cpp

@@ -759,13 +759,15 @@ CompositorBridgeParent::PauseComposition()
   if (!mPaused) {
     mPaused = true;
 
+    TimeStamp now = TimeStamp::Now();
     if (mCompositor) {
       mCompositor->Pause();
+      DidComposite(now, now);
     } else if (mWrBridge) {
       mWrBridge->Pause();
+      NotifyPipelineRendered(mWrBridge->PipelineId(), mWrBridge->GetCurrentEpoch(),
+                             now, now);
     }
-    TimeStamp now = TimeStamp::Now();
-    DidComposite(now, now);
   }
 
   // if anyone's waiting to make sure that composition really got paused, tell them

gfx/layers/wr/WebRenderBridgeParent.h

@@ -170,6 +170,7 @@ public:
 
   void ExtractImageCompositeNotifications(nsTArray<ImageCompositeNotificationInfo>* aNotifications);
 
+  wr::Epoch GetCurrentEpoch() const { return mWrEpoch; }
   wr::IdNamespace GetIdNamespace()
   {
     return mIdNamespace;