ui: No more TestCompositor. Use NullDraw contexts in unit tests.

ui/gl/gl_surface.cc

Index: ui/gl/gl_surface.cc
diff --git a/ui/gl/gl_surface.cc b/ui/gl/gl_surface.cc
index ae324b1bf6f446cbe91de29541196c43632f74ea..3933e4256be6cfce197fd08bb3aa3564d219a157 100644
--- a/ui/gl/gl_surface.cc
+++ b/ui/gl/gl_surface.cc
@@ -127,9 +127,8 @@ void GLSurface::InitializeOneOffForTests(bool disable_drawing) {
 
   bool fallback_to_osmesa = false;
   bool gpu_service_logging = false;
-  bool disable_gl_drawing = disable_drawing;
-  // TODO(danakj): Unit tests do not produce pixel output by default.
-  // bool disable_gl_drawing = true;
+  // Unit tests do not produce pixel output by default.
+  bool disable_gl_drawing = true;
 
   CHECK(InitializeOneOffImplementation(
       impl, fallback_to_osmesa, gpu_service_logging, disable_gl_drawing));