error on the side of safety for empty blobs

If the blob is empty, then try to regenerate it. Using
this method caused a slowdown in Skia perf, so we
added an extra check to allow some empty blobs through
for perf performance. The perf problem was caused by
SKPs generate empty blobs because of font mismatches.
Flutter has shown that scaling from very small to
normal size is not correctly handled by the existing
check. This CL favors correctness over optimizing empty
text blob and always regenerates empty blobs.

https://github.com/flutter/flutter/issues/64936

Change-Id: Ib18ecb684b0af5cf6dce274b6dc09a9c61b17c77
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/319031
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
3 files changed