Bug 1491798- Schedule repaint if WebRender is updated by tab move r=mattwoodrow

dom/ipc/TabChild.cpp

@@ -3210,6 +3210,25 @@ TabChild::InvalidateLayers()
   FrameLayerBuilder::InvalidateAllLayers(lm);
 }
 
+void
+TabChild::SchedulePaint()
+{
+  nsCOMPtr<nsIDocShell> docShell = do_GetInterface(WebNavigation());
+  if (!docShell) {
+    return;
+  }
+
+  // We don't use TabChildBase::GetPresShell() here because that would create
+  // a content viewer if one doesn't exist yet. Creating a content viewer can
+  // cause JS to run, which we want to avoid. nsIDocShell::GetPresShell
+  // returns null if no content viewer exists yet.
+  if (nsCOMPtr<nsIPresShell> presShell = docShell->GetPresShell()) {
+    if (nsIFrame* root = presShell->GetRootFrame()) {
+      root->SchedulePaint();
+    }
+  }
+}
+
 void
 TabChild::ReinitRendering()
 {

dom/ipc/TabChild.h

@@ -540,6 +540,7 @@ public:
 
   void ClearCachedResources();
   void InvalidateLayers();
+  void SchedulePaint();
   void ReinitRendering();
   void ReinitRenderingForDeviceReset();
 

gfx/layers/wr/WebRenderLayerManager.cpp

@@ -561,6 +561,12 @@ WebRenderLayerManager::WrUpdated()
 {
   mWebRenderCommandBuilder.ClearCachedResources();
   DiscardLocalImages();
+
+  if (mWidget) {
+    if (dom::TabChild* tabChild = mWidget->GetOwningTabChild()) {
+      tabChild->SchedulePaint();
+    }
+  }
 }
 
 dom::TabGroup*