Add device to top level N-way canvas.
Review URL: https://codereview.appspot.com/6131062

git-svn-id: http://skia.googlecode.com/svn/trunk@3811 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkNWayCanvas.cpp b/src/utils/SkNWayCanvas.cpp
index 06cf32d..9f6ebc6 100644
--- a/src/utils/SkNWayCanvas.cpp
+++ b/src/utils/SkNWayCanvas.cpp
@@ -7,7 +7,11 @@
  */
 #include "SkNWayCanvas.h"
 
-SkNWayCanvas::SkNWayCanvas() {}
+SkNWayCanvas::SkNWayCanvas(int width, int height) {
+    SkBitmap bm;
+    bm.setConfig(SkBitmap::kNo_Config, width, height);
+    this->setBitmapDevice(bm);
+}
 
 SkNWayCanvas::~SkNWayCanvas() {
     this->removeAll();