Use fast malloc for heap-allocated property tree builder context

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PaintPropertyTreeBuilder_h
 #define PaintPropertyTreeBuilder_h
 
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 class FrameView;
 class LayoutBoxModelObject;
 class LayoutObject;
 
 // The context for PaintPropertyTreeBuilder.
 // It's responsible for bookkeeping tree state in other order, for example, the
 // most recent position container seen.
 struct PaintPropertyTreeBuilderContext {
+  USING_FAST_MALLOC(PaintPropertyTreeBuilderContext);
+
+ public:
   // State that propagates on the containing block chain (and so is adjusted
   // when an absolute or fixed position object is encountered).
   struct ContainingBlockContext {
     // The combination of a transform and paint offset describes a linear space.
     // When a layout object recur to its children, the main context is expected
     // to refer the object's border box, then the callee will derive its own
     // border box by translating the space with its own layout location.
     const TransformPaintPropertyNode* transform = nullptr;
     LayoutPoint paintOffset;
     // Whether newly created children should flatten their inherited transform
@@ skipping 20 matching lines @@
   ContainingBlockContext current;
 
   // Separate context for out-of-flow positioned and fixed positioned elements
   // are needed because they don't use DOM parent as their containing block.
   // These additional contexts normally pass through untouched, and are only
   // copied from the main context when the current element serves as the
   // containing block of corresponding positioned descendants.  Overflow clips
   // are also inherited by containing block tree instead of DOM tree, thus they
   // are included in the additional context too.
   ContainingBlockContext absolutePosition;
-  const LayoutObject* containerForAbsolutePosition = nullptr;
+  const LayoutObject* containerForAbsolutePosition;

[Xianzhu, 2017/03/20 16:20:24]

Why change these?

[pdr., 2017/03/20 16:35:32]

These seem to be required for fast malloc. A few other callsites do this as
well.

 
   ContainingBlockContext fixedPosition;
 
   // This is the same as current.paintOffset except when a floating object has
   // non-block ancestors under its containing block. Paint offsets of the
   // non-block ancestors should not be accumulated for the floating object.
   LayoutPoint paintOffsetForFloat;
 
   // The effect hierarchy is applied by the stacking context tree. It is
   // guaranteed that every DOM descendant is also a stacking context descendant.
   // Therefore, we don't need extra bookkeeping for effect nodes and can
   // generate the effect tree from a DOM-order traversal.
-  const EffectPaintPropertyNode* currentEffect = nullptr;
+  const EffectPaintPropertyNode* currentEffect;
   // Some effects are spatial, i.e. may refer to input pixels outside of output
   // clip. The cull rect for its input shall be derived from its output clip.
   // This variable represents the input cull of current effect, also serves as
   // output clip of child effects that don't have a hard clip.
-  const ClipPaintPropertyNode* inputClipOfCurrentEffect = nullptr;
+  const ClipPaintPropertyNode* inputClipOfCurrentEffect;
 
   // True if a change has forced all properties in a subtree to be updated. This
   // can be set due to paint offset changes or when the structure of the
   // property tree changes (i.e., a node is added or removed).
-  bool forceSubtreeUpdate = false;
+  bool forceSubtreeUpdate;
+
+  PaintPropertyTreeBuilderContext()
+      : containerForAbsolutePosition(nullptr),
+        currentEffect(nullptr),
+        inputClipOfCurrentEffect(nullptr),
+        forceSubtreeUpdate(false) {}
 };
 
 // Creates paint property tree nodes for special things in the layout tree.
 // Special things include but not limit to: overflow clip, transform, fixed-pos,
 // animation, mask, filter, ... etc.
 // It expects to be invoked for each layout tree node in DOM order during
 // InPrePaint phase.
 class PaintPropertyTreeBuilder {
  public:
   void setupInitialContext(PaintPropertyTreeBuilderContext&);
@@ skipping 49 matching lines @@
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
   ALWAYS_INLINE static void updateOutOfFlowContext(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
 };
 
 }  // namespace blink
 
 #endif  // PaintPropertyTreeBuilder_h