This refactor adds a typed iterator class for helping to iterate over
varying registers from packed varyings. We use the same iteration
logic in several places and it has a triple loop, so encapsulating
this into an iterator class keeps it cleaner.
The other change is to use std::stringstream in places where we would
return a std::string.
These refactorings will aid in subsequent work to implement provoking
vertex fixes and to refactor our varying packing algorithm.
BUG=angleproject:754
Change-Id: Id44a1f68ccd4edc3458f1cf514f5eab4b8cd4151
Reviewed-on: https://chromium-review.googlesource.com/309811Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
