Remove GetSharedMainThreadContextProvider from CompositorDependencies.

content/test/fake_compositor_dependencies.cc

Index: content/test/fake_compositor_dependencies.cc
diff --git a/content/test/fake_compositor_dependencies.cc b/content/test/fake_compositor_dependencies.cc
index bdd240ac04c1cad0327ee650791bdc43dd99284b..f379dc930f98172bfbb1bbb80934f093186c7857 100644
--- a/content/test/fake_compositor_dependencies.cc
+++ b/content/test/fake_compositor_dependencies.cc
@@ -85,12 +85,6 @@ FakeCompositorDependencies::GetRendererScheduler() {
   return &renderer_scheduler_;
 }
 
-cc::ContextProvider*
-FakeCompositorDependencies::GetSharedMainThreadContextProvider() {
-  NOTREACHED();
-  return nullptr;
-}
-
 std::unique_ptr<cc::BeginFrameSource>
 FakeCompositorDependencies::CreateExternalBeginFrameSource(int routing_id) {
   double refresh_rate = 200.0;