Support more always-available extensions in ContextNULL.

Add some extensions that are required by the passthrough command decoder
and exposed on all other ANGLE backends.

BUG=781164

Change-Id: Ie83143effd2460122e7a093c658f217fb460d8b2
Reviewed-on: https://chromium-review.googlesource.com/759132
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/renderer/null/ContextNULL.cpp b/src/libANGLE/renderer/null/ContextNULL.cpp
index c9cbb6e..abd5c88 100644
--- a/src/libANGLE/renderer/null/ContextNULL.cpp
+++ b/src/libANGLE/renderer/null/ContextNULL.cpp
@@ -73,7 +73,10 @@
     mExtensions.copyTexture           = true;
     mExtensions.copyCompressedTexture = true;
     mExtensions.textureRectangle      = true;
-    mExtensions.textureUsage          = true;
+    mExtensions.textureUsage           = true;
+    mExtensions.vertexArrayObject      = true;
+    mExtensions.debugMarker            = true;
+    mExtensions.translatedShaderSource = true;
 
     mExtensions.rgb8rgba8 = true;
     mExtensions.textureCompressionDXT1     = true;