Provide SocketStreamHandleInternal::toWebSocketStreamHandle(SocketStreamHandle*).

Provide SocketStreamHandleInternal::toWebSocketStreamHandle(SocketStreamHandle*).
https://bugs.webkit.org/show_bug.cgi?id=78581

Reviewed by Kent Tamura.

Now, there is no way to convert SocketStreamHandle to
WebSocketStreamHandle. In subsequent changes, I'll use this function
in FrameLoaderClientImpl.

* src/SocketStreamHandle.cpp: Remove SocketStreamHandleInternal class declaration.
* src/SocketStreamHandleInternal.h: Move SocketStreamHandleInternal class declaration from SocketStreamHandle.cpp to expose, and add conversion function to WebSocketStreamHandle from SocketStreamHandle.
(WebKit):
(WebCore):
(SocketStreamHandleInternal):
(WebCore::SocketStreamHandleInternal::create):
(WebCore::SocketStreamHandleInternal::toWebSocketStreamHandle):
* WebKit.gyp: Add SocketStreamHandleInternal.h entry.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107782 268f45cc-cd09-0410-ab3c-d52691b4dbfc