Adding android.os.Debug.countInstancesOfClass

- Debug.countInstancesOfClass is just a wrapper on
  dalvik.system.VMDebug.countInstancesOfClass to avoid code from
  depending on the dalvik classes directly

- Existing usages of VMDebug.countInstancesOfClass in ActivityThread
  and ViewDebug are converted to the new Debug.countInstancesOfClass

- Existing use of OpenSSLSocketImpl.instanceCount, which is being
  removed, is converted to Debug.countInstancesOfClass(OpenSSLSocketImpl.class)

Bug: 3015791
Change-Id: Iefa781292d5b82a63bad7254c913a09deb3b7888