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 85ceb2e95a5109150374c74dab9eccfef375b3e8..19d62361176e5c156f1f36f3cc53e7c1a673ca63 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -364,16 +364,22 @@ 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 (!visible_) {
+    TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::CanDraw invisible",
+                         TRACE_EVENT_SCOPE_THREAD);
+    return false;
+  }
+
   if (DrawViewportSize().IsEmpty()) {
     TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::CanDraw empty viewport",
                          TRACE_EVENT_SCOPE_THREAD);
@@ -764,8 +770,7 @@ 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;
   }
 
@@ -944,11 +949,11 @@ 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
   // 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()
@@ -1089,8 +1094,7 @@ 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;
   }
 
@@ -1429,6 +1433,7 @@ void LayerTreeHostImpl::SetExternalDrawConstraints(
   viewport_rect_for_tile_priority_ =
       viewport_rect_for_tile_priority_in_view_space;
   resourceless_software_draw_ = resourceless_software_draw;
+  client_->OnCanDrawStateChanged(CanDraw());
 }
 
 void LayerTreeHostImpl::SetNeedsRedrawRect(const gfx::Rect& damage_rect) {
@@ -1525,8 +1530,7 @@ 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;
   }
 
@@ -1961,6 +1965,7 @@ void LayerTreeHostImpl::SetVisible(bool visible) {
     return;
   visible_ = visible;
   DidVisibilityChange(this, visible_);
+  client_->OnCanDrawStateChanged(CanDraw());
   UpdateTileManagerMemoryPolicy(ActualManagedMemoryPolicy());
 
   // If we just became visible, we have to ensure that we draw high res tiles,
@@ -2785,13 +2790,15 @@ void LayerTreeHostImpl::RequestUpdateForSynchronousInputHandler() {
 
 void LayerTreeHostImpl::SetSynchronousInputHandlerRootScrollOffset(
     const gfx::ScrollOffset& root_offset) {
-  active_tree_->DistributeRootScrollOffset(root_offset);
+  bool changed = active_tree_->DistributeRootScrollOffset(root_offset);
+  if (!changed)
+    return;
+
   client_->SetNeedsCommitOnImplThread();
   // After applying the synchronous input handler's scroll offset, tell it what
   // we ended up with.
   UpdateRootLayerStateForSynchronousInputHandler();
-  // No need to SetNeedsRedraw, this is for WebView and every frame has redraw
-  // requested by the WebView embedder already.
+  SetNeedsRedraw();
 }
 
 void LayerTreeHostImpl::ClearCurrentlyScrollingLayer() {