Update the clang plugin to optionally enforce rules for Blink code.

tools/clang/plugins/ChromeClassTester.h

Index: tools/clang/plugins/ChromeClassTester.h
diff --git a/tools/clang/plugins/ChromeClassTester.h b/tools/clang/plugins/ChromeClassTester.h
index 6b5cdf3577ea3a71d85f87b0995a1af406e94a00..e3d7e3caab209d83eda315c16fc86de14ed7134c 100644
--- a/tools/clang/plugins/ChromeClassTester.h
+++ b/tools/clang/plugins/ChromeClassTester.h
@@ -85,10 +85,14 @@ class ChromeClassTester : public clang::ASTConsumer {
   clang::DiagnosticsEngine& diagnostic_;
 
   // List of banned namespaces.
-  std::vector<std::string> banned_namespaces_;
+  std::set<std::string> banned_namespaces_;
+
+  // List of directories allowed even though their parent directories are in
+  // |banned_directories_|, below.
+  std::set<std::string> allowed_directories_;
 
   // List of banned directories.
-  std::vector<std::string> banned_directories_;
+  std::set<std::string> banned_directories_;
 
   // List of types that we don't check.
   std::set<std::string> ignored_record_names_;