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

net/spdy/spdy_alt_svc_wire_format_test.cc

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/spdy/spdy_alt_svc_wire_format.h"
 
 #include "base/logging.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/platform_test.h"
 
 using ::testing::_;
+using base::StringPiece;
 
 namespace net {
 
 namespace test {
 
 // Expose all private methods of class SpdyAltSvcWireFormat.
 class SpdyAltSvcWireFormatPeer {
  public:
   static void SkipWhiteSpace(StringPiece::const_iterator* c,
                              StringPiece::const_iterator end) {
@@ skipping 564 matching lines @@
     StringPiece input(invalid_input);
     double probability;
     EXPECT_FALSE(test::SpdyAltSvcWireFormatPeer::ParseProbability(
         input.begin(), input.end(), &probability));
   }
 }
 
 }  // namespace
 
 }  // namespace net