[Cronet] Make delaying sending request headers explicit in bidirectional stream

net/http/bidirectional_stream_impl.h

Index: net/http/bidirectional_stream_impl.h
diff --git a/net/http/bidirectional_stream_impl.h b/net/http/bidirectional_stream_impl.h
index 8dff82df9c0df7778b577b003f9b6ed912eeec72..8e019295d283c519256b8c536569456208eb3967 100644
--- a/net/http/bidirectional_stream_impl.h
+++ b/net/http/bidirectional_stream_impl.h
@@ -43,7 +43,9 @@ class NET_EXPORT_PRIVATE BidirectionalStreamImpl {
     // or call BidirectionalStreamImpl::Cancel to cancel the stream.
     // The delegate should not call BidirectionalStreamImpl::Cancel
     // during this callback.
-    virtual void OnStreamReady() = 0;
+    // |request_headers_sent| if true, request headers have been sent. If false,
+    // SendRequestHeaders() needs to be explicitly called.
+    virtual void OnStreamReady(bool request_headers_sent) = 0;
 
     // Called when response headers are received.
     // This is called at most once for the lifetime of a stream.
@@ -90,12 +92,20 @@ class NET_EXPORT_PRIVATE BidirectionalStreamImpl {
   virtual ~BidirectionalStreamImpl();
 
   // Starts the BidirectionalStreamImpl and sends request headers.
+  // |send_request_headers_automatically| if true, request headers will be sent
+  // automatically when stream is negotiated. If false, request headers will be
+  // sent only if until SendRequestHeaders() is invoked or until next
+  // SendData/SendvData.
   virtual void Start(const BidirectionalStreamRequestInfo* request_info,
                      const BoundNetLog& net_log,
-                     bool disable_auto_flush,
+                     bool send_request_headers_automatically,
                      BidirectionalStreamImpl::Delegate* delegate,
                      std::unique_ptr<base::Timer> timer) = 0;
 
+  // Sends request headers to server. This is only required when
+  // |send_request_headers_automatically| is false.
+  virtual void SendRequestHeaders() = 0;
+
   // Reads at most |buf_len| bytes into |buf|. Returns the number of bytes read,
   // ERR_IO_PENDING if the read is to be completed asynchronously, or an error
   // code if any error occurred. If returns 0, there is no more data to read.