Add QuicStrCat.

net/tools/quic/quic_http_response_cache_test.cc

Index: net/tools/quic/quic_http_response_cache_test.cc
diff --git a/net/tools/quic/quic_http_response_cache_test.cc b/net/tools/quic/quic_http_response_cache_test.cc
index d683d399dfc9748c49bd9716a1bfea43a0380526..cfce66d13b5971d8083e9bc0f0418b2257b732b4 100644
--- a/net/tools/quic/quic_http_response_cache_test.cc
+++ b/net/tools/quic/quic_http_response_cache_test.cc
@@ -179,7 +179,7 @@ TEST_F(QuicHttpResponseCacheTest, AddSimpleResponseWithServerPushResources) {
     string path = "/server_push_src" + base::IntToString(i);
     string url = scheme + "://" + request_host + path;
     GURL resource_url(url);
-    string body = "This is server push response body for " + path;
+    string body = QuicStrCat("This is server push response body for ", path);
     SpdyHeaderBlock response_headers;
     response_headers[":version"] = "HTTP/1.1";
     response_headers[":status"] = "200";