First pass at Comment API

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
===================================================================
--- include/core/SkCanvas.h	(revision 9288)
+++ include/core/SkCanvas.h	(working copy)
@@ -852,8 +852,25 @@
         subclasses like SkPicture's recording canvas, that can store the data
         and then play it back later (via another call to drawData).
      */
-    virtual void drawData(const void* data, size_t length);
+    virtual void drawData(const void* data, size_t length) {
+        // do nothing. Subclasses may do something with the data
+    }
 
+    /** Add comments. beginCommentGroup/endCommentGroup open/close a new group. 
+        Each comment added via addComment is notionally attached to its 
+        enclosing group. Top-level comments simply belong to no group.
+     */
+    virtual void beginCommentGroup(const char* description) {
+        // do nothing. Subclasses may do something
+    }
+    virtual void addComment(const char* kywd, const char* value) {
+        // do nothing. Subclasses may do something
+    }
+    virtual void endCommentGroup() {
+        // do nothing. Subclasses may do something
+    }
+
+
     //////////////////////////////////////////////////////////////////////////
 
     /** Get the current bounder object.
@@ -1138,4 +1155,25 @@
     int         fSaveCount;
 };
 
+/** Stack helper class to automatically open and close a comment block
+ */
+class SkAutoCommentBlock : SkNoncopyable {
+public:
+    SkAutoCommentBlock(SkCanvas* canvas, const char* description) {
+        fCanvas = canvas;
+        if (NULL != fCanvas) {
+            fCanvas->beginCommentGroup(description);
+        }
+    }
+
+    ~SkAutoCommentBlock() {
+        if (NULL != fCanvas) {
+            fCanvas->endCommentGroup();
+        }
+    }
+
+private:
+    SkCanvas* fCanvas;
+};
+
 #endif