[chromium] Add destructor to WebPrerender
https://bugs.webkit.org/show_bug.cgi?id=104820

Reviewed by James Robinson.

When making WebPrerender default constructible and assignable, the destructor should have been moved out of WEBKIT_IMPLEMENTATION.

Source/Platform:

* chromium/public/WebPrerender.h:
(WebKit::WebPrerender::~WebPrerender):
(WebPrerender):

Source/WebCore:

Existing WebKit unit tests should test this, as do chromium browser tests.

* platform/chromium/support/WebPrerender.cpp:
(WebKit::WebPrerender::toPrerender):
(WebKit::WebPrerender::reset):


git-svn-id: https://svn.webkit.org/repository/webkit/trunk/Source/Platform/chromium/public@137482 268f45cc-cd09-0410-ab3c-d52691b4dbfc