make egl_native.cc compile on OSX

gpu/gles2_conform_support/native/egl_native.cc

Index: gpu/gles2_conform_support/native/egl_native.cc
diff --git a/gpu/gles2_conform_support/native/egl_native.cc b/gpu/gles2_conform_support/native/egl_native.cc
index 0a3e6d4b4dd5bab14fd020fd8e706f6d8e0dd16b..bf8c7719b9615a16c39087da9ac3f455d061ff9b 100644
--- a/gpu/gles2_conform_support/native/egl_native.cc
+++ b/gpu/gles2_conform_support/native/egl_native.cc
@@ -23,14 +23,14 @@ void GTFNativeDestroyPixmap(EGLNativeDisplayType nativeDisplay,
 EGLImageKHR GTFCreateEGLImageExternal(
     int width, int height, int format,
     float r, float g, float b, float a, void** resource) {
-  return (EGLImageKHR)NULL;
+  return (EGLImageKHR)0;
 }
 
 void GTFDestroyEGLImageExternal(EGLImageKHR image, void* resource) {
 }
 
 const int* GTFQueryFormatsEGLImageExternal(void) {
-  return NULL;
+  return 0;
 }
 
 GTFbool GTFIsAlphaFormatEGLImageExternal(int format) {