Will now DCHECK that test writers start the embedded server before using it.

net/test/embedded_test_server/embedded_test_server.cc

Index: net/test/embedded_test_server/embedded_test_server.cc
diff --git a/net/test/embedded_test_server/embedded_test_server.cc b/net/test/embedded_test_server/embedded_test_server.cc
index 07bad2813faeb12596bfbeab6c32cdb00ae500d0..128597f20e8f80cb2a5bd202c4b03d9a7327a188 100644
--- a/net/test/embedded_test_server/embedded_test_server.cc
+++ b/net/test/embedded_test_server/embedded_test_server.cc
@@ -196,6 +196,7 @@ void EmbeddedTestServer::HandleRequest(HttpConnection* connection,
 }
 
 GURL EmbeddedTestServer::GetURL(const std::string& relative_url) const {
+  DCHECK(Started()) << "You must start the server first.";
   DCHECK(StartsWithASCII(relative_url, "/", true /* case_sensitive */))
       << relative_url;
   return base_url_.Resolve(relative_url);