NativeThemeAndroid should inherit from NativeThemeBase
NativeThemeAndroid currently re-implements every method defined in the
NativeTheme class by duplicating the code, while it didn't actually modify
behavior. By changing its base class to NativeThemeBase, which has most
of the code we need, we only have to override GetSystemColor.
Visually, this lines up Android's button appearance with Linux, as Android's
code hadn't been updated for changing coming in to the general implementation.
It also enables the new checkbox appearance all of Chrome will be switching
too. Removing the old code is being tracked in Issue 133991.