Add WTF_EXPORT to BitVector::OutOfLineBits

Add WTF_EXPORT to BitVector::OutOfLineBits

dllexport/dllimport aren't inherited by nested classes like visibility
attributes are on Posix, and this class has some non-inline methods that
need to get exported.

For example, if ~BitVector gets inlined, we might try calling
OutOfLineBits::destroy across a dll boundry.

BUG=82385
TEST=attempt to build blink_web.dll with Clang on Windows

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176061

[hans, 2014-06-12 20:05:42]

Please take a look.

[Nico, 2014-06-12 20:39:19]

lgtm

Does msvs have ways to force things to be inlined? If so, could you do a local
experiment where you force this call to be inlined and check that things fail in
the same way in the msvs build?

[Reid Kleckner, 2014-06-12 20:50:06]

Yes, there is __forceinline, but you have to build with optimizations for it to
work.  We've done small tests like:

struct __declspec(dllimport) Foo {
  static __forceinline void f() { Bar::g(); }
  struct Bar {
    static void g();
  };
};
int main() {
  Foo::f();
}

$ cl -O2 -c t.cpp -Facl.asm && cat cl.asm
...
        call    ?g@Bar@Foo@@SAXXZ

So the importer calls through to g, which is incorrect if the exporter doesn't
export g.

[hans, 2014-06-12 21:02:17]

The CQ bit was checked by hans@chromium.org

[commit-bot: I haz the power, 2014-06-12 21:03:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hans@chromium.org/338463002/1

[commit-bot: I haz the power, 2014-06-12 23:44:16]

Change committed as 176061