Simplify GrResourceCache/GrDrawingManager flush interaction.

Change-Id: I2442da32a364ec77ccbefc58ceaa62de8e991caf
Reviewed-on: https://skia-review.googlesource.com/152669
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
4 files changed