cc: More consistent reasoning about display list memory usage.

cc/playback/float_clip_display_item.cc

Index: cc/playback/float_clip_display_item.cc
diff --git a/cc/playback/float_clip_display_item.cc b/cc/playback/float_clip_display_item.cc
index 126752a6e0c06475175a67cd67ad28e8bb2da5dd..8b29fc214c55c3cf43492c32d1269591e641d38b 100644
--- a/cc/playback/float_clip_display_item.cc
+++ b/cc/playback/float_clip_display_item.cc
@@ -20,9 +20,8 @@ FloatClipDisplayItem::~FloatClipDisplayItem() {
 void FloatClipDisplayItem::SetNew(const gfx::RectF& clip_rect) {
   clip_rect_ = clip_rect;
 
-  size_t memory_usage = sizeof(gfx::RectF);
   DisplayItem::SetNew(true /* suitable_for_gpu_raster */, 1 /* op_count */,
-                      memory_usage);
+                      0 /* external_memory_usage */);
 }
 
 void FloatClipDisplayItem::Raster(SkCanvas* canvas,
@@ -40,7 +39,7 @@ void FloatClipDisplayItem::AsValueInto(
 
 EndFloatClipDisplayItem::EndFloatClipDisplayItem() {
   DisplayItem::SetNew(true /* suitable_for_gpu_raster */, 0 /* op_count */,
-                      0 /* memory_usage */);
+                      0 /* external_memory_usage */);
 }
 
 EndFloatClipDisplayItem::~EndFloatClipDisplayItem() {