Attempt 3 at:

ui/gfx/compositor/compositor_cc.cc

Index: ui/gfx/compositor/compositor_cc.cc
diff --git a/ui/gfx/compositor/compositor_cc.cc b/ui/gfx/compositor/compositor_cc.cc
index 2ebed681438bc173c99418de34f155c5db2f01ad..3b4412451c8c8304b656e16e9f1425176f5df17c 100644
--- a/ui/gfx/compositor/compositor_cc.cc
+++ b/ui/gfx/compositor/compositor_cc.cc
@@ -22,7 +22,12 @@
 #include "webkit/gpu/webgraphicscontext3d_in_process_impl.h"
 
 namespace {
+
 webkit_glue::WebThreadImpl* g_compositor_thread = NULL;
+
+// If true a context is used that results in no rendering to the screen.
+bool test_context_enabled = false;
+
 }  // anonymous namespace
 
 namespace ui {
@@ -121,9 +126,6 @@ void TextureCC::Draw(const ui::TextureDrawParams& params,
   NOTREACHED();
 }
 
-// static
-bool CompositorCC::test_context_enabled_ = false;
-
 CompositorCC::CompositorCC(CompositorDelegate* delegate,
                            gfx::AcceleratedWidget widget,
                            const gfx::Size& size)
@@ -172,12 +174,6 @@ void CompositorCC::Terminate() {
   }
 }
 
-// static
-void CompositorCC::EnableTestContextIfNecessary() {
-  // TODO: only do this if command line param not set.
-  test_context_enabled_ = true;
-}
-
 Texture* CompositorCC::CreateTexture() {
   NOTREACHED();
   return NULL;
@@ -247,7 +243,7 @@ void CompositorCC::applyScrollDelta(const WebKit::WebSize&) {
 
 WebKit::WebGraphicsContext3D* CompositorCC::createContext3D() {
   WebKit::WebGraphicsContext3D* context;
-  if (test_context_enabled_) {
+  if (test_context_enabled) {
     context = new TestWebGraphicsContext3D();
   } else {
     gfx::GLShareGroup* share_group =
@@ -286,4 +282,15 @@ Compositor* Compositor::Create(CompositorDelegate* owner,
   return new CompositorCC(owner, widget, size);
 }
 
+COMPOSITOR_EXPORT void SetupTestCompositor() {
+  if (!CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kDisableTestCompositor)) {
+    test_context_enabled = true;
+  }
+}
+
+COMPOSITOR_EXPORT void DisableTestCompositor() {
+  test_context_enabled = false;
+}
+
 }  // namespace ui