services/ui: Inject GpuService instance where needed, instead of singleton.

services/ui/public/cpp/gles2_context.h

Index: services/ui/public/cpp/gles2_context.h
diff --git a/services/ui/public/cpp/gles2_context.h b/services/ui/public/cpp/gles2_context.h
index d26499d7494bd5ca61eef01229721555d81ea002..a4e56035352544f96864524bf6a5264aff134b24 100644
--- a/services/ui/public/cpp/gles2_context.h
+++ b/services/ui/public/cpp/gles2_context.h
@@ -25,6 +25,7 @@ class GLES2CmdHelper;
 namespace ui {
 
 class CommandBufferClientImpl;
+class GpuService;
 
 class GLES2Context {
  public:
@@ -35,11 +36,11 @@ class GLES2Context {
   gpu::ContextSupport* context_support() const { return implementation_.get(); }
 
   static std::unique_ptr<GLES2Context> CreateOffscreenContext(
-      const std::vector<int32_t>& attribs);
+      GpuService* gpu_service);
 
  private:
   GLES2Context();
-  bool Initialize(const std::vector<int32_t>& attribs);
+  bool Initialize(GpuService* gpu_service);
 
   std::unique_ptr<CommandBufferClientImpl> command_buffer_client_impl_;
   std::unique_ptr<gpu::CommandBufferProxyImpl> command_buffer_proxy_impl_;