Add stubs for GL_OES_fbo_render_mipmap.

BUG=angle:905

Change-Id: Idd4964bd2d9d07cd98137770e1cc57397f1dd3a6
Reviewed-on: https://chromium-review.googlesource.com/263762
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES.cpp b/src/libANGLE/validationES.cpp
index 8de5ca4..2e2ca84 100644
--- a/src/libANGLE/validationES.cpp
+++ b/src/libANGLE/validationES.cpp
@@ -1735,8 +1735,8 @@
 bool ValidateFramebufferTexture2D(Context *context, GLenum target, GLenum attachment,
                                   GLenum textarget, GLuint texture, GLint level)
 {
-    // Attachments are required to be bound to level 0 in ES2
-    if (context->getClientVersion() < 3 && level != 0)
+    // Attachments are required to be bound to level 0 without ES3 or the GL_OES_fbo_render_mipmap extension
+    if (context->getClientVersion() < 3 && !context->getExtensions().fboRenderMipmap && level != 0)
     {
         context->recordError(Error(GL_INVALID_VALUE));
         return false;