cc: Partial draw without partial swap support.

components/display_compositor/buffer_queue.cc

Index: components/display_compositor/buffer_queue.cc
diff --git a/components/display_compositor/buffer_queue.cc b/components/display_compositor/buffer_queue.cc
index afb40e1a4912accfc68929b8d7b72d70e7ac8cb8..b63833c49a05258f6ea9b5e2801f88ae677f9afe 100644
--- a/components/display_compositor/buffer_queue.cc
+++ b/components/display_compositor/buffer_queue.cc
@@ -67,6 +67,14 @@ void BufferQueue::BindFramebuffer() {
   }
 }
 
+bool BufferQueue::CanPartialDraw(const gfx::Rect& damage) {
+  if (current_surface_)
+    return damage.Contains(current_surface_->damage);
+  if (!available_surfaces_.empty())
+    return damage.Contains(available_surfaces_.back()->damage);
+  return false;
+}
+
 void BufferQueue::CopyBufferDamage(int texture,
                                    int source_texture,
                                    const gfx::Rect& new_damage,
@@ -89,7 +97,7 @@ void BufferQueue::UpdateBufferDamage(const gfx::Rect& damage) {
 
 void BufferQueue::SwapBuffers(const gfx::Rect& damage) {
   if (current_surface_) {
-    if (damage != gfx::Rect(size_)) {
+    if (!damage.Contains(current_surface_->damage)) {
       // Copy damage from the most recently swapped buffer. In the event that
       // the buffer was destroyed and failed to recreate, pick from the most
       // recently available buffer.