Return Error from onMakeCurrent

- Preliminary change for gl_PointCoords fix for Vulkan.

Bug: angleproject:2673
Change-Id: Ie43e8aeccf75a8daa4a137b98292d848522ea2f0
Reviewed-on: https://chromium-review.googlesource.com/1134877
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Luc Ferron <lucferron@chromium.org>
diff --git a/src/libANGLE/renderer/null/ContextNULL.cpp b/src/libANGLE/renderer/null/ContextNULL.cpp
index b288c23..5021986 100644
--- a/src/libANGLE/renderer/null/ContextNULL.cpp
+++ b/src/libANGLE/renderer/null/ContextNULL.cpp
@@ -310,8 +310,9 @@
     return 0;
 }
 
-void ContextNULL::onMakeCurrent(const gl::Context *context)
+gl::Error ContextNULL::onMakeCurrent(const gl::Context *context)
 {
+    return gl::NoError();
 }
 
 gl::Caps ContextNULL::getNativeCaps() const