Some components in the Flutter engine were derived from the forked blink codebase. While the forked components have either been removed or rewritten, the use of the blink namespace has mostly (and inconsistently) remained. This renames the blink namesapce to flutter for consistency. There are no functional changes in this patch.
This patch prepares us to switch sending semantics information over mojom to
using dart:ui directly. Currently the recorded information is dropped on the
floor, but that will improve in future patches.
