Moving gRPC support interfaces out of cronet and into a new component.

components/grpc_support/environment.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_GRPC_SUPPORT_ENVIRONMENT_H_
+#define COMPONENTS_GRPC_SUPPORT_ENVIRONMENT_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/tracked_objects.h"
+
+namespace net {
+class URLRequestContext;
+}
+
+namespace grpc_support {
+
+// Abstract base class for gRPC environment.
+class Environment {
+ public:
+  virtual bool IsOnNetworkThread() = 0;
+  virtual void PostToNetworkThread(const tracked_objects::Location& from_here,
+                                   const base::Closure& task) = 0;
+  virtual net::URLRequestContext* GetURLRequestContext() const = 0;
+  virtual std::string UserAgent() = 0;
+};
+
+}  // namespace grpc_support
+
+#endif  // COMPONENTS_GRPC_SUPPORT_ENVIRONMENT_H_