Add a few stubs so we can link the latest OpenGL ES 2.0 conformance tests

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 02a8ba40a1c9bb6da44a802d9fef615cbe1fc159..0a3e6d4b4dd5bab14fd020fd8e706f6d8e0dd16b 100644
--- a/gpu/gles2_conform_support/native/egl_native.cc
+++ b/gpu/gles2_conform_support/native/egl_native.cc
@@ -20,6 +20,23 @@ void GTFNativeDestroyPixmap(EGLNativeDisplayType nativeDisplay,
                             EGLNativePixmapType nativePixmap) {
 }
 
+EGLImageKHR GTFCreateEGLImageExternal(
+    int width, int height, int format,
+    float r, float g, float b, float a, void** resource) {
+  return (EGLImageKHR)NULL;
+}
+
+void GTFDestroyEGLImageExternal(EGLImageKHR image, void* resource) {
+}
+
+const int* GTFQueryFormatsEGLImageExternal(void) {
+  return NULL;
+}
+
+GTFbool GTFIsAlphaFormatEGLImageExternal(int format) {
+  return GTFfalse;
+}
+
 }  // extern "C"