Remove |using base::StringPiece| from net/spdy header files.

net/spdy/spdy_header_block_test.cc

Index: net/spdy/spdy_header_block_test.cc
diff --git a/net/spdy/spdy_header_block_test.cc b/net/spdy/spdy_header_block_test.cc
index 2e449ba5791cecaa262ba96b3d32a50f9db2c7a1..c7bb2837e1fa6ac7aae0635ea22a28fb82f815c1 100644
--- a/net/spdy/spdy_header_block_test.cc
+++ b/net/spdy/spdy_header_block_test.cc
@@ -19,7 +19,8 @@ using ::testing::ElementsAre;
 
 namespace net {
 
-std::pair<StringPiece, StringPiece> Pair(StringPiece k, StringPiece v) {
+std::pair<base::StringPiece, base::StringPiece> Pair(base::StringPiece k,
+                                                     base::StringPiece v) {
   return make_pair(k, v);
 }