First pass at Comment API

gm/rects.cpp

Index: gm/rects.cpp
===================================================================
--- gm/rects.cpp	(revision 9288)
+++ gm/rects.cpp	(working copy)
@@ -207,10 +207,14 @@
     }
 
     virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        SkAutoCommentBlock acb(canvas, "onDraw");
+
         canvas->translate(20 * SK_Scalar1, 20 * SK_Scalar1);
 
         int testCount = 0;
 
+        canvas->addComment("Test", "Various Paints");
+
         for (int i = 0; i < fPaints.count(); ++i) {
             for (int j = 0; j < fRects.count(); ++j, ++testCount) {
                 canvas->save();
@@ -220,6 +224,8 @@
             }
         }
 
+        canvas->addComment("Test", "Matrices");
+
         SkPaint paint;
         paint.setColor(SK_ColorWHITE);
         paint.setAntiAlias(true);