Add comments to SkRecordDraw to help people follow.

src/core/SkRecordDraw.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkRecordDraw_DEFINED
 #define SkRecordDraw_DEFINED
 
@@ skipping 19 matching lines @@
 
 namespace SkRecords {
 
 // This is an SkRecord visitor that will draw that SkRecord to an SkCanvas.
 class Draw : SkNoncopyable {
 public:
     explicit Draw(SkCanvas* canvas, const SkMatrix* initialCTM = NULL)
         : fInitialCTM(initialCTM ? *initialCTM : canvas->getTotalMatrix())
         , fCanvas(canvas) {}
 
+    // This operator calls methods on the |canvas|. The various draw() wrapper
+    // methods around SkCanvas are defined by the DRAW() macro in
+    // SkRecordDraw.cpp.
     template <typename T> void operator()(const T& r) {
         this->draw(r);
     }
 
 private:
     // No base case, so we'll be compile-time checked that we implement all possibilities.
     template <typename T> void draw(const T&);
 
     const SkMatrix fInitialCTM;
     SkCanvas* fCanvas;
@@ skipping 17 matching lines @@
     }
 
 private:
     const SkRect fClearRect;
     typedef Draw INHERITED;
 };
 
 }  // namespace SkRecords
 
 #endif//SkRecordDraw_DEFINED