Adds missing function

Review URL: https://codereview.appspot.com/6346067

git-svn-id: http://skia.googlecode.com/svn/trunk@4459 2bbb7eff-a529-9590-31e7-b0007b416f81

debugger/SkDebugCanvas.h

@@ -69,6 +69,13 @@ public:
      */
     std::vector<std::string>* getDrawCommandsAsStrings();
 
+    /**
+        Returns length of draw command vector.
+     */
+    int getSize() {
+        return commandVector.size();
+    }
+
     /**
         Toggles the execution of the draw command at index i.
      */