cc: Use a ListContainer for DisplayItemList to reduce allocations.

Currently every DisplayItem is malloced/freed individually. Follow the
pattern used for DrawQuads instead, using ListContainer to allocate
log(n) times instead of once for each item. This replaces each
DisplayFooItem::Create(...) with a default constructor and a
DisplayFooItem::SetNew(...) that must be called on newly constructed
items before they are used.

This patch changes the time to do UpdateLayers (after making
gfx::ImageSkiaReps immutable cuz they dominate times for now) for a
single tab loading spinner from .174ms to .167ms on a linux x620,
giving a 4% reduction in frame record time. I used a mean of 3000
samples in each run to reduce noise.

R=ajuma, enne
BUG=466426

Review URL: https://codereview.chromium.org/1123983002

Cr-Commit-Position: refs/heads/master@{#328797}

1 files changed, 12 insertions, 8 deletions

diff --git a/cc/test/fake_content_layer_client.cc b/cc/test/fake_content_layer_client.cc
index c21d87b..dce5e6e 100644
--- a/cc/test/fake_content_layer_client.cc
+++ b/cc/test/fake_content_layer_client.cc
@@ -78,8 +78,8 @@ void FakeContentLayerClient::PaintContentsToDisplayList(
   SkPictureRecorder recorder;
   skia::RefPtr<SkCanvas> canvas;
   skia::RefPtr<SkPicture> picture;
-  display_list->AppendItem(
-      ClipDisplayItem::Create(clip, std::vector<SkRRect>()));
+  auto* item = display_list->CreateAndAppendItem<ClipDisplayItem>();
+  item->SetNew(clip, std::vector<SkRRect>());
 
   for (RectPaintVector::const_iterator it = draw_rects_.begin();
        it != draw_rects_.end(); ++it) {
@@ -90,21 +90,24 @@ void FakeContentLayerClient::PaintContentsToDisplayList(
     canvas->drawRectCoords(draw_rect.x(), draw_rect.y(), draw_rect.width(),
                            draw_rect.height(), paint);
     picture = skia::AdoptRef(recorder.endRecordingAsPicture());
-    display_list->AppendItem(DrawingDisplayItem::Create(picture));
+    auto* item = display_list->CreateAndAppendItem<DrawingDisplayItem>();
+    item->SetNew(picture.Pass());
   }
 
   for (BitmapVector::const_iterator it = draw_bitmaps_.begin();
        it != draw_bitmaps_.end(); ++it) {
     if (!it->transform.IsIdentity()) {
-      display_list->AppendItem(TransformDisplayItem::Create(it->transform));
+      auto* item = display_list->CreateAndAppendItem<TransformDisplayItem>();
+      item->SetNew(it->transform);
     }
     canvas = skia::SharePtr(
         recorder.beginRecording(it->bitmap.width(), it->bitmap.height()));
     canvas->drawBitmap(it->bitmap, it->point.x(), it->point.y(), &it->paint);
     picture = skia::AdoptRef(recorder.endRecordingAsPicture());
-    display_list->AppendItem(DrawingDisplayItem::Create(picture));
+    auto* item = display_list->CreateAndAppendItem<DrawingDisplayItem>();
+    item->SetNew(picture.Pass());
     if (!it->transform.IsIdentity()) {
-      display_list->AppendItem(EndTransformDisplayItem::Create());
+      display_list->CreateAndAppendItem<EndTransformDisplayItem>();
     }
   }
 
@@ -118,12 +121,13 @@ void FakeContentLayerClient::PaintContentsToDisplayList(
           recorder.beginRecording(gfx::RectFToSkRect(draw_rect)));
       canvas->drawRect(gfx::RectFToSkRect(draw_rect), paint);
       picture = skia::AdoptRef(recorder.endRecordingAsPicture());
-      display_list->AppendItem(DrawingDisplayItem::Create(picture));
+      auto* item = display_list->CreateAndAppendItem<DrawingDisplayItem>();
+      item->SetNew(picture.Pass());
       draw_rect.Inset(1, 1);
     }
   }
 
-  display_list->AppendItem(EndClipDisplayItem::Create());
+  display_list->CreateAndAppendItem<EndClipDisplayItem>();
 }
 
 bool FakeContentLayerClient::FillsBoundsCompletely() const { return false; }