Use a Transformer for UserData as well, to avoid always copying arrays and dictionaries
https://bugs.webkit.org/show_bug.cgi?id=139896

Reviewed by Darin Adler.

* Shared/UserData.cpp:
(WebKit::shouldTransform):
(WebKit::UserData::transform):
* Shared/UserData.h:
(WebKit::UserData::Transformer::~Transformer):
* UIProcess/WebProcessProxy.cpp:
(WebKit::WebProcessProxy::apiObjectByConvertingToHandles):
* WebProcess/WebProcess.cpp:
(WebKit::WebProcess::apiObjectByConvertingFromHandles):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@177685 268f45cc-cd09-0410-ab3c-d52691b4dbfc