Add QuicStrCat.

net/quic/core/quic_stream_sequencer_buffer_test.cc

Index: net/quic/core/quic_stream_sequencer_buffer_test.cc
diff --git a/net/quic/core/quic_stream_sequencer_buffer_test.cc b/net/quic/core/quic_stream_sequencer_buffer_test.cc
index 855fe1608b53968f3cc86483024572f0309e92e6..d3b59239b74ebc4e9b1376795d97ce5acf7ef6c2 100644
--- a/net/quic/core/quic_stream_sequencer_buffer_test.cc
+++ b/net/quic/core/quic_stream_sequencer_buffer_test.cc
@@ -144,10 +144,10 @@ TEST_F(QuicStreamSequencerBufferTest, OnStreamDataInvalidSource) {
   QuicTime t = clock_.ApproximateNow();
   EXPECT_EQ(QUIC_STREAM_SEQUENCER_INVALID_STATE,
             buffer_->OnStreamData(800, source, t, &written, &error_details_));
-  EXPECT_EQ(
-      0u, error_details_.find("QuicStreamSequencerBuffer error: OnStreamData()"
-                              " dest == nullptr: false"
-                              " source == nullptr: true"));
+  EXPECT_EQ(0u, error_details_.find(QuicStrCat(
+                    "QuicStreamSequencerBuffer error: OnStreamData() "
+                    "dest == nullptr: ",
+                    false, " source == nullptr: ", true)));
 }
 
 TEST_F(QuicStreamSequencerBufferTest, OnStreamDataWithOverlap) {