RenderWidgetHostNSViewBridge is in content/common instead of content/public/... because it has several content-internal imports.

These imports are for serializing/deserializing Blink types (e.g, blink::Cursor and blink::WebInputEvent).

This bug is to change RenderWidgetHostNSViewCocoa (and associated code) to use the appropriate ui types (e.g, ui::NativeCursor and ui::Event). Once that is done, RenderWidgetHostNSViewBridge can be moved to be public.

Further refactoring after that point could potentially merge RenderWidgetHostNSViewBridge and BridgedNativeWidget as a single "NSView across mojo" class (this would involve an almost-complete rewrite of RenderWidgetHostNSViewMac, and should be weighed against simply switching to Aura).