Update from https://crrev.com/328418

tools/clang/plugins/ChromeClassTester.cpp

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // A general interface for filtering and only acting on classes in Chromium C++
 // code.
 
 #include "ChromeClassTester.h"
 
 #include <algorithm>
 
 #include "clang/AST/AST.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/SourceManager.h"
 
 #ifdef LLVM_ON_UNIX
 #include <sys/param.h>
 #endif
 
 using namespace clang;
+using chrome_checker::Options;
 
 namespace {
 
 bool ends_with(const std::string& one, const std::string& two) {
   if (two.size() > one.size())
     return false;
 
   return one.compare(one.size() - two.size(), two.size(), two) == 0;
 }
 
 }  // namespace
 
-ChromeClassTester::ChromeClassTester(CompilerInstance& instance)
-    : instance_(instance),
+ChromeClassTester::ChromeClassTester(CompilerInstance& instance,
+                                     const Options& options)
+    : options_(options),
+      instance_(instance),
       diagnostic_(instance.getDiagnostics()) {
   BuildBannedLists();
 }
 
 ChromeClassTester::~ChromeClassTester() {}
 
 void ChromeClassTester::HandleTagDeclDefinition(TagDecl* tag) {
   pending_class_decls_.push_back(tag);
 }
 
@@ skipping 43 matching lines @@
     CheckChromeEnum(enum_location, enum_decl);
   }
 }
 
 void ChromeClassTester::emitWarning(SourceLocation loc,
                                     const char* raw_error) {
   FullSourceLoc full(loc, instance().getSourceManager());
   std::string err;
   err = "[chromium-style] ";
   err += raw_error;
-  // TODO(dcheng): Re-enable -Werror for these diagnostics on Windows once all
-  // the pre-existing warnings are cleaned up. https://crbug.com/467287
-  DiagnosticIDs::Level level =
-#if !defined(LLVM_ON_WIN32)
-      diagnostic().getWarningsAsErrors() ?
-      DiagnosticIDs::Error :
-#endif
-      DiagnosticIDs::Warning;
+
+  DiagnosticIDs::Level level = getErrorLevel() == DiagnosticsEngine::Error
+      ? DiagnosticIDs::Error : DiagnosticIDs::Warning;
+
   unsigned id = diagnostic().getDiagnosticIDs()->getCustomDiagID(level, err);
   DiagnosticBuilder builder = diagnostic().Report(full, id);
+
 }
 
 bool ChromeClassTester::InBannedDirectory(SourceLocation loc) {
   if (instance().getSourceManager().isInSystemHeader(loc))
     return true;
 
   std::string filename;
   if (!GetFilename(loc, &filename)) {
     // If the filename cannot be determined, simply treat this as a banned
     // location, instead of going through the full lookup process.
     return true;
   }
 
   // We need to special case scratch space; which is where clang does its
   // macro expansion. We explicitly want to allow people to do otherwise bad
   // things through macros that were defined due to third party libraries.
   if (filename == "<scratch space>")
     return true;
 
   // Don't complain about autogenerated protobuf files.
   if (ends_with(filename, ".pb.h")) {
     return true;
   }
 
 #if defined(LLVM_ON_UNIX)
-  // We need to munge the paths so that they are relative to the repository
-  // srcroot. We first resolve the symlinktastic relative path and then
-  // remove our known srcroot from it if needed.
+  // Resolve the symlinktastic relative path and make it absolute.
   char resolvedPath[MAXPATHLEN];
   if (realpath(filename.c_str(), resolvedPath)) {
     filename = resolvedPath;
   }
 #endif
 
 #if defined(LLVM_ON_WIN32)
   std::replace(filename.begin(), filename.end(), '\\', '/');
+
+  // On Posix, realpath() has made the path absolute.  On Windows, this isn't
+  // necessarily true, so prepend a '/' to the path to make sure the
+  // banned_directories_ loop below works correctly.
+  // This turns e.g. "gen/dir/file.cc" to "/gen/dir/file.cc" which lets the
+  // "/gen/" banned_dir work.
+  // This seems simpler than converting to utf16, calling GetFullPathNameW(),
+  // and converting back to utf8.
+  filename.insert(filename.begin(), '/');
 #endif
 
   for (const std::string& banned_dir : banned_directories_) {
     // If any of the banned directories occur as a component in filename,
     // this file is rejected.
     assert(banned_dir.front() == '/' && "Banned dir must start with '/'");
     assert(banned_dir.back() == '/' && "Banned dir must end with '/'");
 
     if (filename.find(banned_dir) != std::string::npos)
       return true;
@@ skipping 143 matching lines @@
   PresumedLoc ploc = source_manager.getPresumedLoc(spelling_location);
   if (ploc.isInvalid()) {
     // If we're in an invalid location, we're looking at things that aren't
     // actually stated in the source.
     return false;
   }
 
   *filename = ploc.getFilename();
   return true;
 }
+
+DiagnosticsEngine::Level ChromeClassTester::getErrorLevel() {
+  if (options_.warn_only)
+    return DiagnosticsEngine::Warning;
+
+  return diagnostic().getWarningsAsErrors() ? DiagnosticsEngine::Error
+                                            : DiagnosticsEngine::Warning;
+}