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

services/ui/public/cpp/context_provider.cc

Index: services/ui/public/cpp/context_provider.cc
diff --git a/services/ui/public/cpp/context_provider.cc b/services/ui/public/cpp/context_provider.cc
index bed839e227e6f76497e15bf6ca8a99bc964dcca3..ec1991c3a4030e3cece7b22e0a2d5f1aafdbfc13 100644
--- a/services/ui/public/cpp/context_provider.cc
+++ b/services/ui/public/cpp/context_provider.cc
@@ -11,10 +11,11 @@
 
 namespace ui {
 
-ContextProvider::ContextProvider() {}
+ContextProvider::ContextProvider(GpuService* gpu_service)
+    : gpu_service_(gpu_service) {}
 
 bool ContextProvider::BindToCurrentThread() {
-  context_ = GLES2Context::CreateOffscreenContext(std::vector<int32_t>());
+  context_ = GLES2Context::CreateOffscreenContext(gpu_service_);
   return !!context_;
 }