Add Network.setSendRequestIdHeader and use it in headless

third_party/WebKit/Source/core/inspector/InspectorNetworkAgent.cpp

Index: third_party/WebKit/Source/core/inspector/InspectorNetworkAgent.cpp
diff --git a/third_party/WebKit/Source/core/inspector/InspectorNetworkAgent.cpp b/third_party/WebKit/Source/core/inspector/InspectorNetworkAgent.cpp
index 5eb6b5baff7e606c0ef78f6a94ed99d7f75db685..cd1597daa2ac8ead1665a8872c5c1a4a2598a8bb 100644
--- a/third_party/WebKit/Source/core/inspector/InspectorNetworkAgent.cpp
+++ b/third_party/WebKit/Source/core/inspector/InspectorNetworkAgent.cpp
@@ -695,6 +695,10 @@ void InspectorNetworkAgent::willSendRequest(
     request.addHTTPHeaderField(
         HTTPNames::X_DevTools_Emulate_Network_Conditions_Client_Id,
         AtomicString(m_hostId));
+
+  request.setHTTPHeaderField(
+      HTTPNames::X_DevTools_Request_Id,
+      AtomicString(IdentifiersFactory::requestId(identifier)));

[Sami, 2017/02/27 12:39:07]

This won't be set for blocked requests (didBlockRequest). I'm assuming that's
okay?

[alex clarke (OOO till 29th), 2017/02/27 13:51:16]

I think that's fine because the protocol handlers will never see the fetch if
it's canceled by DevTools.

 }
 
 void InspectorNetworkAgent::markResourceAsCached(unsigned long identifier) {