Use the new name for SkFrontBufferedStream

Bug: skbug.com/10154
Test: CtsGraphicsTestCases

The API is being moved to a new file and renamed. Use the new API.

Remove an unncessary FIXME and comment in Movie.cpp. The hardcoded 6 is
fine, and the ownership is obvious now that we use smart pointers.

Change-Id: I79657626ccbd5fe2616d546c617d591928064106