Revert "Skip flush in GrDrawingManager if the specifed proxy doesn't have any work"

This reverts commit 4187ac5e4717b08a2f302baa1697ec91bddc6ab6.

Reason for revert: test if this is causing the angle GM image diffs

Original change's description:
> Skip flush in GrDrawingManager if the specifed proxy doesn't have any work
> 
> This is rather ham-fisted but I would like to have a short-term fix for the "always-flush" perf regressions.
> 
> Change-Id: Id359ad5a01a290e7e6c06f7ccc1c385ad47d2c06
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206277
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=egdaniel@google.com,bsalomon@google.com,robertphillips@google.com

Change-Id: I19ea23a6b8e3985353fc1ebaf974513bb922e9f2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206694
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed