Enforce constant size and device scale factor for surfaces

cc/surfaces/surface.cc

Index: cc/surfaces/surface.cc
diff --git a/cc/surfaces/surface.cc b/cc/surfaces/surface.cc
index 00de0c24878222656afe6be81862306cb3d699d2..125d089c934b181a169c1ef7c69a3940e2265465 100644
--- a/cc/surfaces/surface.cc
+++ b/cc/surfaces/surface.cc
@@ -24,10 +24,10 @@ namespace cc {
 static const int kFrameIndexStart = 2;
 
 Surface::Surface(
-    const SurfaceId& id,
+    const SurfaceInfo& surface_info,
     base::WeakPtr<CompositorFrameSinkSupport> compositor_frame_sink_support)
-    : surface_id_(id),
-      previous_frame_surface_id_(id),
+    : surface_info_(surface_info),
+      previous_frame_surface_id_(surface_info.id()),
       compositor_frame_sink_support_(std::move(compositor_frame_sink_support)),
       surface_manager_(compositor_frame_sink_support_->surface_manager()),
       frame_index_(kFrameIndexStart),
@@ -58,7 +58,18 @@ void Surface::Close() {
 void Surface::QueueFrame(CompositorFrame frame,
                          const base::Closure& callback,
                          const WillDrawCallback& will_draw_callback) {
-  if (closed_) {
+  bool reject_frame = closed_;
+
+  gfx::Size frame_size = frame.render_pass_list.back()->output_rect.size();
+  float device_scale_factor = frame.metadata.device_scale_factor;
+
+  if (frame_size != surface_info_.size_in_pixels() ||
+      device_scale_factor != surface_info_.device_scale_factor()) {
+    DLOG(FATAL) << "Rejected CompositorFrame that violates surface invariants.";

[Fady Samuel, 2017/05/17 00:40:50]

Is this necessary? Don't we already check this in CompositorFrameSinkSupport?

[Saman Sami, 2017/05/17 00:55:17]

We don't. I guess you are confusing it with the check for SurfaceInfo validity?

+    reject_frame = true;
+  }
+
+  if (reject_frame) {
     if (compositor_frame_sink_support_) {
       ReturnedResourceArray resources;
       TransferableResource::ReturnResources(frame.resource_list, &resources);
@@ -307,7 +318,7 @@ void Surface::RunWillDrawCallback(const gfx::Rect& damage_rect) {
   if (!active_frame_data_ || active_frame_data_->will_draw_callback.is_null())
     return;
 
-  active_frame_data_->will_draw_callback.Run(surface_id_.local_surface_id(),
+  active_frame_data_->will_draw_callback.Run(surface_id().local_surface_id(),
                                              damage_rect);
 }