Add stubs for a NULL renderer.

BUG=angleproject:1468

Change-Id: I2ed2b65a4b6f6ea3dda61c0467aef95e407cd38c
Reviewed-on: https://chromium-review.googlesource.com/388844
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index f48e5ec..053aa81 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -313,6 +313,9 @@
   if (angle_enable_vulkan) {
     defines += [ "ANGLE_ENABLE_VULKAN" ]
   }
+  if (angle_enable_null) {
+    defines += [ "ANGLE_ENABLE_NULL" ]
+  }
   defines += [
     "GL_GLEXT_PROTOTYPES",
     "EGL_EGLEXT_PROTOTYPES",
@@ -417,6 +420,10 @@
     sources += rebase_path(gles_gypi.libangle_vulkan_sources, ".", "src")
   }
 
+  if (angle_enable_null) {
+    sources += rebase_path(gles_gypi.libangle_null_sources, ".", "src")
+  }
+
   if (is_debug) {
     defines += [ "ANGLE_GENERATE_SHADER_DEBUG_INFO" ]
   }