android webview: allow cc to fail hardware draw

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index e1aae1a6a36a5c37a98f3e6286119390ea718905..cca67d0571747f452a6054121aacc227d39df184 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -365,14 +365,14 @@ bool LayerTreeHostImpl::CanDraw() const {
   DCHECK(output_surface_);
 
   // TODO(boliu): Make draws without root_layer work and move this below
-  // draw_and_swap_full_viewport_every_frame check. Tracked in crbug.com/264967.
+  // |resourceless_software_draw_| check. Tracked in crbug.com/264967.
   if (!active_tree_->root_layer()) {
     TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::CanDraw no root layer",
                          TRACE_EVENT_SCOPE_THREAD);
     return false;
   }
 
-  if (output_surface_->capabilities().draw_and_swap_full_viewport_every_frame)
+  if (resourceless_software_draw_)
     return true;
 
   if (DrawViewportSize().IsEmpty()) {
@@ -765,8 +765,7 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
     TRACE_EVENT0("cc",
                  "LayerTreeHostImpl::CalculateRenderPasses::EmptyDamageRect");
     frame->has_no_damage = true;
-    DCHECK(!output_surface_->capabilities()
-               .draw_and_swap_full_viewport_every_frame);
+    DCHECK(!resourceless_software_draw_);
     return DRAW_SUCCESS;
   }
 
@@ -945,11 +944,11 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
       draw_result = DRAW_ABORTED_MISSING_HIGH_RES_CONTENT;
   }
 
-  // When this capability is set we don't have control over the surface the
+  // When resourceless software draw, we don't have control over the surface the

[danakj, 2015/10/22 18:49:23]

"When doing a resourceless..."

[boliu, 2015/10/22 21:50:08]

Done.

   // compositor draws to, so even though the frame may not be complete, the
   // previous frame has already been potentially lost, so an incomplete frame is
   // better than nothing, so this takes highest precidence.
-  if (output_surface_->capabilities().draw_and_swap_full_viewport_every_frame)
+  if (resourceless_software_draw_)
     draw_result = DRAW_SUCCESS;
 
 #if DCHECK_IS_ON()
@@ -1090,8 +1089,7 @@ DrawResult LayerTreeHostImpl::PrepareToDraw(FrameData* frame) {
 
   DrawResult draw_result = CalculateRenderPasses(frame);
   if (draw_result != DRAW_SUCCESS) {
-    DCHECK(!output_surface_->capabilities()
-               .draw_and_swap_full_viewport_every_frame);
+    DCHECK(!resourceless_software_draw_);
     return draw_result;
   }
 
@@ -1448,6 +1446,11 @@ void LayerTreeHostImpl::SetExternalDrawConstraints(
     SetFullRootLayerDamage();
     SetNeedsRedraw();
   }
+
+  if (resourceless_software_draw_changed) {
+    client_->OnResourcelessSoftareDrawStateChanged(resourceless_software_draw);

[danakj, 2015/10/22 18:49:23]

The only thing I can see maybe being better is that it's not obvious to me what
order things happen when you read the code. Like will the scheduler always be
told about the draw state changing before drawing, and then will it always be
reset back to false at the right times?

Another way to approach it might be to pass resourceless_software_draw_ to
OnDrawForOutputSurface(), then have the scheduler set it true from that, and
reset it to false after the draw completes.

What do you think Brian?

[boliu, 2015/10/22 18:58:08]

Yep. Always reset back to false after the OnDraw
I vote for doing that (although fixing up tests is going to be more involved)

Might be debatable some other params here should be passed in from OnDraw as
well, but let's have that debate later.

[brianderson, 2015/10/22 20:53:35]

I'd vote for an argument as well. I didn't realize this flag would toggle that
often.

+    client_->OnCanDrawStateChanged(CanDraw());
+  }
 }
 
 void LayerTreeHostImpl::SetNeedsRedrawRect(const gfx::Rect& damage_rect) {
@@ -1556,8 +1559,7 @@ void LayerTreeHostImpl::DrawLayers(FrameData* frame) {
 
   if (frame->has_no_damage) {
     TRACE_EVENT_INSTANT0("cc", "EarlyOut_NoDamage", TRACE_EVENT_SCOPE_THREAD);
-    DCHECK(!output_surface_->capabilities()
-               .draw_and_swap_full_viewport_every_frame);
+    DCHECK(!resourceless_software_draw_);
     return;
   }