add SkCanvas constructor that explicitly creates no_config with dimensions

src/utils/debugger/SkDebugCanvas.cpp

Index: src/utils/debugger/SkDebugCanvas.cpp
diff --git a/src/utils/debugger/SkDebugCanvas.cpp b/src/utils/debugger/SkDebugCanvas.cpp
index 1c3e26e6437248ea1e7673c822b99858e033289d..32a65709546258c03ac6443a1923b9e1b661a441 100644
--- a/src/utils/debugger/SkDebugCanvas.cpp
+++ b/src/utils/debugger/SkDebugCanvas.cpp
@@ -14,14 +14,8 @@
 #include "SkDevice.h"
 #include "SkXfermode.h"
 
-static SkBitmap make_noconfig_bm(int width, int height) {
-    SkBitmap bm;
-    bm.setConfig(SkBitmap::kNo_Config, width, height);
-    return bm;
-}
-
 SkDebugCanvas::SkDebugCanvas(int width, int height)
-        : INHERITED(make_noconfig_bm(width, height))
+        : INHERITED(width, height)
         , fWidth(width)
         , fHeight(height)
         , fFilter(false)