In WebKit, we often write Foo::ensureBar function which lazily
initializes m_bar and returns a raw pointer or a raw reference to m_bar.
Such a return value is safe to use for the duration of a member function
call in Foo so long as m_bar is const so that it never gets unset or
updated with a new value once it's initialized.
This PR adds support for recognizing these types of functions and
treating its return value as a safe origin of a function argument
(including "this") or a local variable.
Treat member function calls to ref() and incrementCheckedPtrCount() as
trivial so that a function which returns RefPtr/Ref out of a raw
reference / pointer is also considered trivial.
This PR introduces alpha.webkit.UncheckedCallArgsChecker which detects a
function argument which is a raw reference or a raw pointer to a
CheckedPtr capable object.
