Remove offscreen compositor contexts.

cc/output/renderer.cc

Index: cc/output/renderer.cc
diff --git a/cc/output/renderer.cc b/cc/output/renderer.cc
index b0c4a60dbb7d36550c63995ffe66f1a3ce6edf06..e12d69e945dea6f29d665d55705193b59efcbf9f 100644
--- a/cc/output/renderer.cc
+++ b/cc/output/renderer.cc
@@ -17,7 +17,6 @@ bool Renderer::IsContextLost() {
 RendererCapabilitiesImpl::RendererCapabilitiesImpl()
     : best_texture_format(RGBA_8888),
       allow_partial_texture_updates(false),
-      using_offscreen_context3d(false),
       max_texture_size(0),
       using_shared_memory_resources(false),
       using_partial_swap(false),
@@ -32,7 +31,6 @@ RendererCapabilitiesImpl::~RendererCapabilitiesImpl() {}
 RendererCapabilities RendererCapabilitiesImpl::MainThreadCapabilities() const {
   return RendererCapabilities(best_texture_format,
                               allow_partial_texture_updates,
-                              using_offscreen_context3d,
                               max_texture_size,
                               using_shared_memory_resources);
 }