Add more components_unittests to GN build

components/error_page/renderer/BUILD.gn

Index: components/error_page/renderer/BUILD.gn
diff --git a/components/error_page/renderer/BUILD.gn b/components/error_page/renderer/BUILD.gn
index bafaada3d30d11c59218f92eaf366e17b909adf0..83c49a173d455a6e11a0e4e798a18d9fc65c340b 100644
--- a/components/error_page/renderer/BUILD.gn
+++ b/components/error_page/renderer/BUILD.gn
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-static_library("renderer") {
+source_set("renderer") {
   sources = [
     "net_error_helper_core.cc",
     "net_error_helper_core.h",
@@ -20,3 +20,14 @@ static_library("renderer") {
     "//url",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "net_error_helper_core_unittest.cc",
+  ]
+  deps = [
+    ":renderer",
+    "//testing/gtest",
+  ]
+}