add peekPixels to SkCanvas and SkSurface

gm/imagefiltersclipped.cpp

Index: gm/imagefiltersclipped.cpp
diff --git a/gm/imagefiltersclipped.cpp b/gm/imagefiltersclipped.cpp
index 82873ab3729df60748218dd288d25f9b9b7f92bf..331ea49061160b929cdf9655e0e79f77dda5200d 100644
--- a/gm/imagefiltersclipped.cpp
+++ b/gm/imagefiltersclipped.cpp
@@ -35,8 +35,7 @@ protected:
 
     void make_checkerboard() {
         fCheckerboard.allocN32Pixels(64, 64);
-        SkBitmapDevice device(fCheckerboard);
-        SkCanvas canvas(&device);
+        SkCanvas canvas(fCheckerboard);
         canvas.clear(0x00000000);
         SkPaint darkPaint;
         darkPaint.setColor(0xFF404040);
@@ -58,10 +57,9 @@ protected:
     void make_gradient_circle(int width, int height) {
         SkScalar x = SkIntToScalar(width / 2);
         SkScalar y = SkIntToScalar(height / 2);
-        SkScalar radius = SkScalarMul(SkMinScalar(x, y), SkIntToScalar(4) / SkIntToScalar(5));
+        SkScalar radius = SkMinScalar(x, y) * 0.8f;
         fGradientCircle.allocN32Pixels(width, height);
-        SkBitmapDevice device(fGradientCircle);
-        SkCanvas canvas(&device);
+        SkCanvas canvas(fGradientCircle);
         canvas.clear(0x00000000);
         SkColor colors[2];
         colors[0] = SK_ColorWHITE;