Region Op Fuzzer

Also: assert Region IRects don't contain Sentinel value.
Also: Region fuzzer can't produce Sentinel value.

Change-Id: Ia33c7eeb9ef2c46b3da4a025d85de8a0406c3c0c
Reviewed-on: https://skia-review.googlesource.com/119011
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 69ed2d4..a200f6a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1767,6 +1767,7 @@
       "fuzz/FuzzParsePath.cpp",
       "fuzz/FuzzPathMeasure.cpp",
       "fuzz/FuzzPathop.cpp",
+      "fuzz/FuzzRegionOp.cpp",
       "fuzz/fuzz.cpp",
       "fuzz/oss_fuzz/FuzzAnimatedImage.cpp",
       "fuzz/oss_fuzz/FuzzImage.cpp",