Add fuzzer test for preg_parser

components/policy/core/common/BUILD.gn

Index: components/policy/core/common/BUILD.gn
diff --git a/components/policy/core/common/BUILD.gn b/components/policy/core/common/BUILD.gn
index 17a586048824a59d4f09aaee003e300ed6eeb9d2..c49a7da6cde74bd081505dfbb467c211d659fad8 100644
--- a/components/policy/core/common/BUILD.gn
+++ b/components/policy/core/common/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
+import("//testing/libfuzzer/fuzzer_test.gni")
 
 group("common") {
   if (is_component_build) {
@@ -347,3 +348,17 @@ source_set("unit_tests") {
     "//testing/gtest",
   ]
 }
+
+if (is_win || is_chromeos) {

[Oliver Chang, 2017/04/13 00:25:23]

I wasn't aware that libFuzzer is supported on either of these platforms... How
did you run this?

ClusterFuzz also won't be able to pick up these fuzzers and fuzz them
continuously -- is it possible to build this on linux?

[ljusten (tachyonic), 2017/04/13 11:17:14]

ChromeOS is still Linux, confusingly they're not mutually exclusive. The flag is
set if you add target_os = "chromeos" to args.gn. I was hoping that ClusterFuzz
compiled in that configuration as well. If not, I can change preg_parser to
compile on Linux instead of ChromeOS, but I'm hesitant since it's not used.

[Oliver Chang, 2017/04/13 19:58:24]

thanks for explaining. we don't have any libFuzzer builders that build with
target_os = "chromeos", so please let this compile on Linux.

If always building preg_parser on Linux is a concern, maybe this can be done
only if (use_libfuzzer || use_afl) ?

+  fuzzer_test("preg_parser_fuzzer") {
+    sources = [
+      "preg_parser_fuzzer.cc",
+    ]
+    seed_corpus = "//chrome/test/data/policy/gpo/fuzzer_corpus"
+    dict = "//chrome/test/data/policy/gpo/fuzzer.dict"
+    deps = [
+      ":internal",
+      "//base",
+    ]
+  }
+}