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

net/url_request/url_request_context.h

Index: net/url_request/url_request_context.h
diff --git a/net/url_request/url_request_context.h b/net/url_request/url_request_context.h
index 5c3542843d8b452a1edf0f2a0e0643115e48b216..843124e062f9a51e5cf1a4a23d94282d53a507b7 100644
--- a/net/url_request/url_request_context.h
+++ b/net/url_request/url_request_context.h
@@ -238,6 +238,8 @@ class NET_EXPORT URLRequestContext
     return enable_referrer_policy_header_;
   }
 
+  void DetachFromThread();
+
  private:
   // ---------------------------------------------------------------------------
   // Important: When adding any new members below, consider whether they need to