Create Stubs For Unimplemented Extensions

Create context and validation stubs for unimplemented extensions. This
will allow us to use an autogeneration script in the future to generate
entry_points_gles_2_0_ext.cpp.

Bug:angleproject:2263
Change-Id: If3ad3ebd823d65085c7f143cce9e09187e65d4da
Reviewed-on: https://chromium-review.googlesource.com/998440
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES2.cpp b/src/libANGLE/validationES2.cpp
index 8260719..bb164ef 100644
--- a/src/libANGLE/validationES2.cpp
+++ b/src/libANGLE/validationES2.cpp
@@ -2419,6 +2419,16 @@
     return true;
 }
 
+bool ValidateGetPointervRobustANGLERobustANGLE(Context *context,
+                                               GLenum pname,
+                                               GLsizei bufSize,
+                                               GLsizei *length,
+                                               void **params)
+{
+    UNIMPLEMENTED();
+    return false;
+}
+
 bool ValidateBlitFramebufferANGLE(Context *context,
                                   GLint srcX0,
                                   GLint srcY0,