Add Network.setSendRequestIdHeader and use it in headless

headless/test/headless_browser_test.h

Index: headless/test/headless_browser_test.h
diff --git a/headless/test/headless_browser_test.h b/headless/test/headless_browser_test.h
index 1a258ceccb33d93bad481fa22f0b9451e8aa4fe9..f2d0cca3f63110ef7ca60babe8f6e07857e834cc 100644
--- a/headless/test/headless_browser_test.h
+++ b/headless/test/headless_browser_test.h
@@ -117,6 +117,10 @@ class HeadlessAsyncDevTooledBrowserTest : public HeadlessBrowserTest,
   // are processed (e.g. in a callback).
   virtual void RunDevTooledTest() = 0;
 
+  // Returns the protocol handlers to construct the browser with.  By default
+  // the map returned is empty.
+  virtual ProtocolHandlerMap GetProtocolHandlers();
+
  protected:
   void RunTest();