[regexp] add fuzzer support for regexp parser and compiler.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 3f247ae58721804860dbd3273bc30772cf0f0965..eef2f19702373b7db90c4bbdf47052de2e0fe622 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1953,3 +1953,21 @@ source_set("parser_fuzzer") {
     ":toolchain",
   ]
 }
+
+source_set("regexp_fuzzer") {
+  sources = [
+    "test/fuzzer/regexp.cc",
+  ]
+
+  deps = [
+    ":fuzzer_support",
+  ]
+
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [ "//build/config/compiler:no_chromium_code" ]
+  configs += [
+    ":internal_config",
+    ":features",
+    ":toolchain",
+  ]
+}