cc: Make property trees support resourceless draw mode

cc/trees/property_tree_builder.cc

Index: cc/trees/property_tree_builder.cc
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index 0a7fa29d3cabb16eb19fa29855e1f6d0f704edf3..e9edebf9ddb99c4cb947cfbc9b4e85effa4d4c48 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -138,6 +138,12 @@ void AddClipNodeIfNeeded(const DataForRecursion<LayerType>& data_from_ancestor,
   if (layer_clips_subtree)
     layers_are_clipped = true;
 
+  // Without surfaces, all non-viewport clips have to be applied using layer
+  // clipping.
+  bool layers_are_clipped_when_surfaces_disabled =
+      layer_clips_subtree ||
+      parent->data.layers_are_clipped_when_surfaces_disabled;
+
   bool applies_clip =
       AppliesClip(layer, data_from_ancestor, ancestor_clips_subtree);
   bool parent_applies_clip =
@@ -153,6 +159,8 @@ void AddClipNodeIfNeeded(const DataForRecursion<LayerType>& data_from_ancestor,
   if (!requires_node) {

[jaydasika, 2015/10/16 21:27:09]

In the resourceless draw mode case, can we not just create clip nodes when
layer_clips_subtree = true as we don't have to bother about render surfaces?

[ajuma, 2015/10/16 22:40:41]

It's true that these are the only clips we have to apply in resourceless mode.
But when we're building trees, we need trees that can support both modes without
requiring a rebuild when the mode changes (since the mode can change arbitrarily
on the compositor thread). So, for example, a single set of trees built on the
main thread and then committed to the compositor thread might be used for a
resourceless draw, then a regular draw, and then another resourceless draw.

     data_for_children->clip_tree_parent = parent_id;
     DCHECK_EQ(layers_are_clipped, parent->data.layers_are_clipped);
+    DCHECK_EQ(layers_are_clipped_when_surfaces_disabled,
+              parent->data.layers_are_clipped_when_surfaces_disabled);
   } else {
     LayerType* transform_parent = data_for_children->transform_tree_parent;
     if (layer->position_constraint().is_fixed_position() &&
@@ -200,6 +208,8 @@ void AddClipNodeIfNeeded(const DataForRecursion<LayerType>& data_from_ancestor,
     node.data.resets_clip = has_unclipped_surface || !parent_applies_clip;
     node.data.target_is_clipped = data_for_children->target_is_clipped;
     node.data.layers_are_clipped = layers_are_clipped;
+    node.data.layers_are_clipped_when_surfaces_disabled =
+        layers_are_clipped_when_surfaces_disabled;
 
     data_for_children->clip_tree_parent =
         data_for_children->clip_tree->Insert(node, parent_id);