[fuzzing] adding libprotobuf-mutator BUILD file

third_party/libprotobuf-mutator/BUILD.gn

Index: third_party/libprotobuf-mutator/BUILD.gn
diff --git a/third_party/libprotobuf-mutator/BUILD.gn b/third_party/libprotobuf-mutator/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..0950a05a75d062770809c8a02e3474459d0c1369
--- /dev/null
+++ b/third_party/libprotobuf-mutator/BUILD.gn
@@ -0,0 +1,19 @@
+# Copyright 2017 The Chromium Authors. All rights reserved.
+config("include_config") {
+  include_dirs = [ "src/" ]
+}
+
+source_set("libprotobuf-mutator") {
+  testonly = true
+  configs += [ ":include_config" ]
+  public_configs = [ ":include_config" ]
+  sources = [
+    "src/src/binary_format.cc",
+    "src/src/libfuzzer/libfuzzer_mutator.cc",
+    "src/src/mutator.cc",
+    "src/src/text_format.cc",
+  ]
+  deps = [
+    "//third_party/protobuf:protobuf_full",
+  ]
+}