guarded change to SkImageGenerator to make getInfo() const

tests/SurfaceTest.cpp

Index: tests/SurfaceTest.cpp
diff --git a/tests/SurfaceTest.cpp b/tests/SurfaceTest.cpp
index 9ce9d5fbe83042e357226fa9a080cac37027c027..6142af9ed12649e02af442bd00189ed4b45f0903 100644
--- a/tests/SurfaceTest.cpp
+++ b/tests/SurfaceTest.cpp
@@ -67,11 +67,8 @@ enum ImageType {
 #include "SkImageGenerator.h"
 
 class EmptyGenerator : public SkImageGenerator {
-protected:
-    bool onGetInfo(SkImageInfo* info) SK_OVERRIDE {
-        *info = SkImageInfo::Make(0, 0, kN32_SkColorType, kPremul_SkAlphaType);
-        return true;
-    }
+public:
+    EmptyGenerator() : SkImageGenerator(SkImageInfo::MakeN32Premul(0, 0)) {}
 };
 
 static void test_empty_image(skiatest::Reporter* reporter) {