Clang style plugin: add warn-only option and use it on Windows

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 ed65050d499d76424af42a19877829e5598f2cd9..6b5cdf3577ea3a71d85f87b0995a1af406e94a00 100644
--- a/tools/clang/plugins/ChromeClassTester.h
+++ b/tools/clang/plugins/ChromeClassTester.h
@@ -8,6 +8,7 @@
 #include <set>
 #include <vector>
 
+#include "Options.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/Frontend/CompilerInstance.h"
@@ -16,7 +17,8 @@
 // headers to subclasses which implement CheckChromeClass().
 class ChromeClassTester : public clang::ASTConsumer {
  public:
-  explicit ChromeClassTester(clang::CompilerInstance& instance);
+  ChromeClassTester(clang::CompilerInstance& instance,
+                    const chrome_checker::Options& options);
   virtual ~ChromeClassTester();
 
   // clang::ASTConsumer:
@@ -25,6 +27,8 @@ class ChromeClassTester : public clang::ASTConsumer {
 
   void CheckTag(clang::TagDecl*);
 
+  clang::DiagnosticsEngine::Level getErrorLevel();
+
  protected:
   clang::CompilerInstance& instance() { return instance_; }
   clang::DiagnosticsEngine& diagnostic() { return diagnostic_; }
@@ -50,6 +54,9 @@ class ChromeClassTester : public clang::ASTConsumer {
   // implementation (.cc, .cpp, .mm) file.
   bool InImplementationFile(clang::SourceLocation location);
 
+  // Options.
+  const chrome_checker::Options options_;
+
  private:
   void BuildBannedLists();