adjust size of new apply-filter gm

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/1395303003
diff --git a/gm/spritebitmap.cpp b/gm/spritebitmap.cpp
index 0d467ea..5cf0ece 100644
--- a/gm/spritebitmap.cpp
+++ b/gm/spritebitmap.cpp
@@ -154,7 +154,7 @@
     }
 
     SkISize onISize() override {
-        return SkISize::Make(640, 480);
+        return SkISize::Make(780, 780);
     }
 
     void onDraw(SkCanvas* canvas) override {