cc: More consistent reasoning about display list memory usage.

cc/playback/compositing_display_item.cc

Index: cc/playback/compositing_display_item.cc
diff --git a/cc/playback/compositing_display_item.cc b/cc/playback/compositing_display_item.cc
index 2cd4f4073adc384b54bbc9583276854d585f6b85..31365b5881c22392077744219f114eca52d6c179 100644
--- a/cc/playback/compositing_display_item.cc
+++ b/cc/playback/compositing_display_item.cc
@@ -31,10 +31,9 @@ void CompositingDisplayItem::SetNew(uint8_t alpha,
   color_filter_ = cf;
 
   // TODO(pdr): Include color_filter's memory here.
-  size_t memory_usage =
-      sizeof(float) + sizeof(bool) + sizeof(SkRect) + sizeof(SkXfermode::Mode);
+  size_t external_memory_usage = 0;
   DisplayItem::SetNew(true /* suitable_for_gpu_raster */, 1 /* op_count */,
-                      memory_usage);
+                      external_memory_usage);
 }
 
 void CompositingDisplayItem::Raster(
@@ -61,7 +60,7 @@ void CompositingDisplayItem::AsValueInto(
 
 EndCompositingDisplayItem::EndCompositingDisplayItem() {
   DisplayItem::SetNew(true /* suitable_for_gpu_raster */, 0 /* op_count */,
-                      0 /* memory_usage */);
+                      0 /* external_memory_usage */);
 }
 
 EndCompositingDisplayItem::~EndCompositingDisplayItem() {