Change DebugCanvas API to not encourage memory leaks

debugger/QT/SkDebuggerGUI.h

Index: debugger/QT/SkDebuggerGUI.h
diff --git a/debugger/QT/SkDebuggerGUI.h b/debugger/QT/SkDebuggerGUI.h
index 3f445500c7801a7c8e18c94080d3d0ce5c644801..9cc06256faa042da348de70d825183d6bc987fb6 100644
--- a/debugger/QT/SkDebuggerGUI.h
+++ b/debugger/QT/SkDebuggerGUI.h
@@ -336,12 +336,12 @@ private:
     /**
         Populates the list widget with the vector of strings passed in.
      */
-    void setupListWidget(SkTArray<SkString>* commands, SkTDArray<size_t>* offsets);
+    void setupListWidget(const SkTArray<SkString>& commands, const SkTDArray<size_t>& offsets);
 
     /**
         Populates the combo box widget with the vector of strings passed in.
      */
-    void setupComboBox(SkTArray<SkString>* command);
+    void setupComboBox(const SkTArray<SkString>& command);
 
     /**
         Fills in the overview pane with text