Move third_party/pkg/package_config to pkg_tested.

Closes #24092

[email protected]

Review URL: https://codereview.chromium.org//1296093003 .

Author: whesse

DEPS

@@ -240,7 +240,7 @@ deps = {
   Var("dart_root") + "/third_party/observatory_pub_packages":
      (Var("github_mirror") % "observatory_pub_packages")
       + Var("observatory_pub_packages_rev"),
-  Var("dart_root") + "/third_party/pkg/package_config":
+  Var("dart_root") + "/third_party/pkg_tested/package_config":
       (Var("github_mirror") % "package_config") +
       Var("package_config_tag"),
   Var("dart_root") + "/third_party/pkg/path":

pkg/compiler/pubspec.yaml

@@ -21,7 +21,7 @@ dev_dependencies:
 #
 # dependency_overrides:
 #   package_config:
-#     path: ../../third_party/pkg/package_config
+#     path: ../../third_party/pkg_tested/package_config
 #   path:
 #     path: ../../third_party/pkg/path
 #   charcode: