Export WebSocketHandshake{Request, Response}Info methods.

BLINK_PLATFORM_EXPORT was missing from constructors and destructors
of WebSocketHandshakeRequestInfo and WebSocketHandshakeResponseInfo.
This CL fixes the problem.

BUG=310405
R=tkent

Review URL: https://codereview.chromium.org/87413003

git-svn-id: svn://svn.chromium.org/blink/trunk@162684 bbb929c8-8fbe-4397-9dbb-9b2b20218538