<third_party/WebKit> Fix building with MacOSX10.10.sdk.

RenderThemeChromiumMac.mm:
There is no implicit conversion from int to NSControlSize anymore.

ScrollAnimatorMac.mm updated as done in WebKit:
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@164767 268f45cc-cd09-0410-ab3c-d52691b4dbfc

ScrollbarThemeMacOverlayAPI.mm updated as done in WebKit:
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161397 268f45cc-cd09-0410-ab3c-d52691b4dbfc

WebScrollbarTheme.mm:
Avoid compiler warning and error about comparing/passing different enums.

Change-Id: I6d9f864427a32192049792bb7395ae0abe1a07d6
Reviewed-by: Michael Bruning <michael.bruning@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
<chromium> Fix building with MacOSX10.10.sdk.

The compiler shipping with newer SDKs is more restrictive
with regards to type conversion. It is not accepted
anymore to pass nil (nullptr) for NSUInteger or BOOL.

Change-Id: I15fbfe480aab42e505cec0c6fa47feed718f31c1
Reviewed-by: Michael Bruning <michael.bruning@digia.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>