Use HttpRequestHeaders for extra_headers.
BUG=22588

Review URL: http://codereview.chromium.org/1604011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@45096 0039d316-1c4b-4281-b951-d872f2087c98

• base/string_util.cc[diff]
• net/http/http_auth_handler.h[diff]
• net/http/http_auth_sspi_win.h[diff]
• net/http/http_basic_stream.h[diff]
• net/http/http_cache.h[diff]
• net/http/http_cache_transaction.cc[diff]
• net/http/http_cache_unittest.cc[diff]
• net/http/http_network_layer_unittest.cc[diff]
• net/http/http_network_transaction.cc[diff]
• net/http/http_network_transaction_unittest.cc[diff]
• net/http/http_request_headers.cc[diff]
• net/http/http_request_headers.h[diff]
• net/http/http_request_headers_unittest.cc[diff]
• net/http/http_request_info.h[diff]
• net/http/http_stream.h[diff]
• net/http/http_stream_parser.h[diff]
• net/http/http_transaction.h[diff]
• net/http/http_transaction_unittest.h[diff]
• net/http/http_util.cc[diff]
• net/http/http_util.h[diff]
• net/http/http_vary_data.cc[diff]
• net/http/http_vary_data.h[diff]
• net/http/http_vary_data_unittest.cc[diff]
• net/http/partial_data.cc[diff]
• net/http/partial_data.h[diff]
• net/spdy/spdy_network_transaction_unittest.cc[diff]
• net/spdy/spdy_session.cc[diff]
• net/spdy/spdy_session.h[diff]
• net/url_request/url_request_http_job.cc[diff]