Support MSAA in the picture debugger

Add radio buttons for setting the GL sample count to 0 ("off"), 4 or
16.

Change the default mode of the GL widget to MSAA4. Previous behavior
corresponded to "off".

BUG=1459
R=robertphillips@google.com

Author: kkinnunen@nvidia.com

Review URL: https://chromiumcodereview.appspot.com/21752002

git-svn-id: http://skia.googlecode.com/svn/trunk@10509 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/debugger/QT/SkCanvasWidget.h b/debugger/QT/SkCanvasWidget.h
index 0dcb470..3308613 100644
--- a/debugger/QT/SkCanvasWidget.h
+++ b/debugger/QT/SkCanvasWidget.h
@@ -36,6 +36,10 @@
 
     void setWidgetVisibility(WidgetType type, bool isHidden);
 
+#if SK_SUPPORT_GPU
+    void setGLSampleCount(int sampleCount);
+#endif
+
     /** Zooms the canvas by scale with the transformation centered at the widget point (px, py). */
     void zoom(float scale, int px, int py);