Rename websocket_handshake_handler.* to websocket_handshake_challenge.*

Simplify the calling convention of ComputeSecWebSocketAccept to just return a string, and add a test for it.

BUG=
TEST=net_unittests

Review URL: https://codereview.chromium.org/683033003

Cr-Commit-Position: refs/heads/master@{#304996}
diff --git a/net/net.gypi b/net/net.gypi
index 337f016..cc9ff357 100644
--- a/net/net.gypi
+++ b/net/net.gypi
@@ -1236,8 +1236,8 @@
       'websockets/websocket_frame_parser.h',
       'websockets/websocket_handshake_constants.cc',
       'websockets/websocket_handshake_constants.h',
-      'websockets/websocket_handshake_handler.cc',
-      'websockets/websocket_handshake_handler.h',
+      'websockets/websocket_handshake_challenge.cc',
+      'websockets/websocket_handshake_challenge.h',
       'websockets/websocket_handshake_request_info.cc',
       'websockets/websocket_handshake_request_info.h',
       'websockets/websocket_handshake_response_info.cc',
@@ -1709,7 +1709,7 @@
       'websockets/websocket_extension_parser_test.cc',
       'websockets/websocket_frame_parser_test.cc',
       'websockets/websocket_frame_test.cc',
-      'websockets/websocket_handshake_handler_test.cc',
+      'websockets/websocket_handshake_challenge_test.cc',
       'websockets/websocket_handshake_stream_create_helper_test.cc',
       'websockets/websocket_inflater_test.cc',
       'websockets/websocket_stream_test.cc',