cc: Fix overlay damage tracking bug

cc/output/overlay_processor.cc

Index: cc/output/overlay_processor.cc
diff --git a/cc/output/overlay_processor.cc b/cc/output/overlay_processor.cc
index 43a064fb6e8fd5bb9c2ed11e6fa08e6caaa5de1c..40d6da6c25f3064e4a1d5b5c229ea7ad9060a690 100644
--- a/cc/output/overlay_processor.cc
+++ b/cc/output/overlay_processor.cc
@@ -26,11 +26,18 @@ void OverlayProcessor::Initialize() {
 
 OverlayProcessor::~OverlayProcessor() {}
 
+gfx::Rect OverlayProcessor::GetAndResetOverlayDamage() {
+  gfx::Rect result = overlay_damage_rect_;
+  overlay_damage_rect_ = gfx::Rect();
+  return result;
+}
+
 bool OverlayProcessor::ProcessForCALayers(
     ResourceProvider* resource_provider,
     RenderPassList* render_passes,
+    OverlayCandidateList* overlay_candidates,
     CALayerOverlayList* ca_layer_overlays,
-    OverlayCandidateList* overlay_candidates) {
+    gfx::Rect* damage_rect) {
   RenderPass* root_render_pass = render_passes->back().get();
 
   OverlayCandidateValidator* overlay_validator =
@@ -48,18 +55,43 @@ bool OverlayProcessor::ProcessForCALayers(
   // list.
   overlay_candidates->clear();
   render_passes->back()->quad_list.clear();
+  overlay_damage_rect_ = root_render_pass->output_rect;
+  *damage_rect = gfx::Rect();
   return true;
 }
 
 void OverlayProcessor::ProcessForOverlays(ResourceProvider* resource_provider,
                                           RenderPassList* render_passes,
                                           OverlayCandidateList* candidates,
+                                          CALayerOverlayList* ca_layer_overlays,
                                           gfx::Rect* damage_rect) {
+  // First attempt to process for CALayers.
+  if (ProcessForCALayers(resource_provider, render_passes, candidates,
+                         ca_layer_overlays, damage_rect)) {
+    return;
+  }
+
+  // Only if that fails, attempt hardware overlay strategies.
   for (const auto& strategy : strategies_) {
-    if (strategy->Attempt(resource_provider, render_passes, candidates,
-                          damage_rect)) {
-      return;
+    if (!strategy->Attempt(resource_provider, render_passes, candidates))
+      continue;
+
+    // Subtract on-top overlays from the damage rect, unless the overlays use
+    // the backbuffer as their content (in which case, add their combined rect
+    // back to the damage at the end).
+    gfx::Rect output_surface_overlay_damage_rect;
+    for (const OverlayCandidate& overlay : *candidates) {
+      if (overlay.plane_z_order > 0) {
+        const gfx::Rect overlay_display_rect =
+            ToEnclosedRect(overlay.display_rect);
+        overlay_damage_rect_.Union(overlay_display_rect);
+        damage_rect->Subtract(overlay_display_rect);
+        if (overlay.use_output_surface_for_resource)
+          output_surface_overlay_damage_rect.Union(overlay_display_rect);
+      }
     }
+    damage_rect->Union(output_surface_overlay_damage_rect);
+    return;
   }
 }