Regex fuzzer: Change the region boundaries

Changes the interval boundaries to exclude the first delimiter
that encloses a region.

Change-Id: Ia9186e584d9038b4220cad11d418fa9881e51e8d
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/60346
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Alastair Donaldson <afdx@google.com>
Commit-Queue: Alastair Donaldson <afdx@google.com>

fuzzers/tint_regex_fuzzer/util.h

@@ -0,0 +1,33 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef FUZZERS_TINT_REGEX_FUZZER_UTIL_H_
+#define FUZZERS_TINT_REGEX_FUZZER_UTIL_H_
+
+#include <random>
+
+namespace tint {
+namespace fuzzers {
+namespace regex_fuzzer {
+
+inline size_t GetRandomIntFromRange(size_t lower_bound,
+                                    size_t upper_bound,
+                                    std::mt19937& generator) {
+  std::uniform_int_distribution<size_t> dist(lower_bound, upper_bound);
+  return dist(generator);
+}
+}  // namespace regex_fuzzer
+}  // namespace fuzzers
+}  // namespace tint
+#endif  // FUZZERS_TINT_REGEX_FUZZER_UTIL_H_