First pass at Comment API

src/core/SkPicturePlayback.cpp

Index: src/core/SkPicturePlayback.cpp
===================================================================
--- src/core/SkPicturePlayback.cpp	(revision 8806)
+++ src/core/SkPicturePlayback.cpp	(working copy)
@@ -847,6 +847,18 @@
                 canvas.drawData(reader.skip(length), length);
                 // skip handles padding the read out to a multiple of 4
             } break;
+            case BEGIN_GROUP: {
+                const char* desc = reader.readString();
+                canvas.beginGroup(desc);
+            } break;
+            case COMMENT: {
+                const char* kywd = reader.readString();
+                const char* value = reader.readString();
+                canvas.addComment(kywd, value);
+            } break;
+            case END_GROUP: {
+                canvas.endGroup();
+            } break;
             case DRAW_OVAL: {
                 const SkPaint& paint = *getPaint(reader);
                 canvas.drawOval(reader.skipT<SkRect>(), paint);