[BlackBerry] Assertions and assumptions in BackingStoreClient around m_frame and m_frame->view() are invalid
https://bugs.webkit.org/show_bug.cgi?id=86096

Reviewed by Rob Buis.
Patch by Antonio Gomes <agomes@rim.com>

A Frame's FrameView has always to be checked since it is
a volatile object, and gets created and destroyed all the time.

We have been facing a particular issue, where during our automated
interaction tests, the main frame object was being pinch zoomed in
the middle of it creation, and WebKit thread was blocked by a mutex.
In practice, it is a case that would not be possible in a real
world scenario, but shows that the ASSERTs are bogus regardless.

* WebKitSupport/BackingStoreClient.cpp:
(BlackBerry::WebKit::BackingStoreClient::scrollPosition):
(BlackBerry::WebKit::BackingStoreClient::setScrollPosition):
(BlackBerry::WebKit::BackingStoreClient::maximumScrollPosition):
(BlackBerry::WebKit::BackingStoreClient::viewportSize):
(BlackBerry::WebKit::BackingStoreClient::transformedViewportSize):
(BlackBerry::WebKit::BackingStoreClient::visibleContentsRect):
(BlackBerry::WebKit::BackingStoreClient::contentsSize):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@116657 268f45cc-cd09-0410-ab3c-d52691b4dbfc