[Extensions] Build fix

Fixes linking errors when building with component=shared_library.

undefined reference to 'WebKit::WebScopedMicrotaskSuppression::initialize()'
undefined reference to 'WebKit::WebFrame::frameForCurrentContext()'
undefined reference to 'WebKit::WebScopedMicrotaskSuppression::reset()'
undefined reference to 'WebKit::failedAssertion(char const*, int, char const*, char const*)'
undefined reference to 'AnnotateHappensAfter'
undefined reference to 'AnnotateHappensBefore'
undefined reference to 'AnnotateHappensAfter'