cc: Partial draw without partial swap support.

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index 612c31564878454e01636cf365f22a615440907e..1340e9a4045d60bc01107014182115ca445939ed 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -2447,9 +2447,9 @@ void GLRenderer::FinishDrawingFrame() {
     pending_sync_queries_.push_back(std::move(current_sync_query_));
   }
 
-  swap_buffer_rect_.Union(current_frame()->root_damage_rect);
+  damage_rect_.Union(current_frame()->root_damage_rect);
   if (overdraw_feedback_)
-    FlushOverdrawFeedback(swap_buffer_rect_);
+    FlushOverdrawFeedback(damage_rect_);
 
   if (use_swap_with_bounds_)
     swap_content_bounds_ = current_frame()->root_content_bounds;
@@ -2617,22 +2617,24 @@ void GLRenderer::SwapBuffers(std::vector<ui::LatencyInfo> latency_info) {
   OutputSurfaceFrame output_frame;
   output_frame.latency_info = std::move(latency_info);
   output_frame.size = surface_size;
+  output_frame.damage_rect = damage_rect_;
   if (use_swap_with_bounds_) {
     output_frame.content_bounds = std::move(swap_content_bounds_);
   } else if (use_partial_swap_) {
     // If supported, we can save significant bandwidth by only swapping the
     // damaged/scissored region (clamped to the viewport).
-    swap_buffer_rect_.Intersect(gfx::Rect(surface_size));
+    gfx::Rect swap_buffer_rect = damage_rect_;
+    swap_buffer_rect.Intersect(gfx::Rect(surface_size));
     int flipped_y_pos_of_rect_bottom = surface_size.height() -
-                                       swap_buffer_rect_.y() -
-                                       swap_buffer_rect_.height();
+                                       swap_buffer_rect.y() -
+                                       swap_buffer_rect.height();
     output_frame.sub_buffer_rect =
-        gfx::Rect(swap_buffer_rect_.x(),
+        gfx::Rect(swap_buffer_rect.x(),
                   FlippedRootFramebuffer() ? flipped_y_pos_of_rect_bottom
-                                           : swap_buffer_rect_.y(),
-                  swap_buffer_rect_.width(), swap_buffer_rect_.height());
-  } else if (swap_buffer_rect_.IsEmpty() && allow_empty_swap_) {
-    output_frame.sub_buffer_rect = swap_buffer_rect_;
+                                           : swap_buffer_rect.y(),
+                  swap_buffer_rect.width(), swap_buffer_rect.height());
+  } else if (damage_rect_.IsEmpty() && allow_empty_swap_) {
+    output_frame.sub_buffer_rect = gfx::Rect();
   }
 
   swapping_overlay_resources_.push_back(std::move(pending_overlay_resources_));
@@ -2640,7 +2642,7 @@ void GLRenderer::SwapBuffers(std::vector<ui::LatencyInfo> latency_info) {
 
   output_surface_->SwapBuffers(std::move(output_frame));
 
-  swap_buffer_rect_ = gfx::Rect();
+  damage_rect_ = gfx::Rect();
 }
 
 void GLRenderer::SwapBuffersComplete() {