Add SpdyString alias for std::string in net/spdy.

net/spdy/header_coalescer_test.cc

Index: net/spdy/header_coalescer_test.cc
diff --git a/net/spdy/header_coalescer_test.cc b/net/spdy/header_coalescer_test.cc
index f0f696bc183b9ec11e5e1839a1e5fcfa1a3f4d6f..a9587612ea91548c1f6f2122c84daae50ac11630 100644
--- a/net/spdy/header_coalescer_test.cc
+++ b/net/spdy/header_coalescer_test.cc
@@ -4,8 +4,7 @@
 
 #include "header_coalescer.h"
 
-#include <string>
-
+#include "net/spdy/platform/api/spdy_string.h"
 #include "net/spdy/platform/api/spdy_string_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -41,7 +40,7 @@ TEST_F(HeaderCoalescerTest, EmptyHeaderKey) {
 TEST_F(HeaderCoalescerTest, HeaderBlockTooLarge) {
   // 3 byte key, 256 * 1024 - 40 byte value, 32 byte overhead:
   // less than 256 * 1024 bytes in total.
-  std::string data(256 * 1024 - 40, 'a');
+  SpdyString data(256 * 1024 - 40, 'a');
   header_coalescer_.OnHeader("foo", data);
   EXPECT_FALSE(header_coalescer_.error_seen());