Remove extensions_tests.gyp[i]

extensions/utility/BUILD.gn

Index: extensions/utility/BUILD.gn
diff --git a/extensions/utility/BUILD.gn b/extensions/utility/BUILD.gn
index 5f9923a5eda1e5696e2acf05553ec5e84843595d..9a29a68fd83a8dde91930e9aa704858b7bd11b2d 100644
--- a/extensions/utility/BUILD.gn
+++ b/extensions/utility/BUILD.gn
@@ -23,3 +23,20 @@ source_set("utility") {
     "//skia",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "unpacker_unittest.cc",
+  ]
+  deps = [
+    ":utility",
+    "//base",
+    "//extensions:test_support",
+    "//extensions/common",
+    "//extensions/strings",
+    "//testing/gtest",
+    "//third_party/zlib:zip",
+    "//ui/base",
+  ]
+}