ui: Enable virtual contexts for linux

gpu/command_buffer/service/gl_context_virtual.h

Index: gpu/command_buffer/service/gl_context_virtual.h
diff --git a/gpu/command_buffer/service/gl_context_virtual.h b/gpu/command_buffer/service/gl_context_virtual.h
index d8cf77f8adc562611daf1e8570d8f96754cb2879..1d82d5ac784287faae16c0345bf39216939dde09 100644
--- a/gpu/command_buffer/service/gl_context_virtual.h
+++ b/gpu/command_buffer/service/gl_context_virtual.h
@@ -31,8 +31,6 @@ class GPU_EXPORT GLContextVirtual : public gfx::GLContext {
       gfx::GLContext* shared_context,
       base::WeakPtr<gles2::GLES2Decoder> decoder);
 
-  gfx::Display* display();
-
   // Implement GLContext.
   bool Initialize(gfx::GLSurface* compatible_surface,
                   gfx::GpuPreference gpu_preference) override;
@@ -56,7 +54,6 @@ class GPU_EXPORT GLContextVirtual : public gfx::GLContext {
 
  private:
   scoped_refptr<gfx::GLContext> shared_context_;
-  gfx::Display* display_;
   base::WeakPtr<gles2::GLES2Decoder> decoder_;
 
   DISALLOW_COPY_AND_ASSIGN(GLContextVirtual);