Add comments to SkRecordDraw to help people follow.

src/core/SkRecordDraw.cpp

Index: src/core/SkRecordDraw.cpp
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index 07c02b6a3d90ae45759d5ecadf265acc38a52a51..560607937d071f0a3ea4feb4c43f596daca781b1 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -33,6 +33,9 @@ void SkRecordDraw(const SkRecord& record,
             if (callback && callback->abortDrawing()) {
                 return;
             }
+            // This visit call uses the SkRecords::Draw::operator() to call
+            // methods on the |canvas|, wrapped by methods defined with the
+            // DRAW() macro.
             record.visit<void>(ops[i], draw);
         }
     } else {
@@ -42,6 +45,9 @@ void SkRecordDraw(const SkRecord& record,
             if (callback && callback->abortDrawing()) {
                 return;
             }
+            // This visit call uses the SkRecords::Draw::operator() to call
+            // methods on the |canvas|, wrapped by methods defined with the
+            // DRAW() macro.
             record.visit<void>(i, draw);
         }
     }