Added a base::Callback interface to FilePathWatcher.

base/files/file_path_watcher.cc

Index: base/files/file_path_watcher.cc
diff --git a/base/files/file_path_watcher.cc b/base/files/file_path_watcher.cc
index 086da1e6968c542f7b5632e47d7727d87beeb060..dd2b37fc78d80a937c00afcb803cfc784970047b 100644
--- a/base/files/file_path_watcher.cc
+++ b/base/files/file_path_watcher.cc
@@ -13,6 +13,33 @@
 namespace base {
 namespace files {
 
+namespace {
+
+// A delegate implementation for the callback interface.
+class FilePathWatcherDelegate : public base::files::FilePathWatcher::Delegate {
+ public:
+  explicit FilePathWatcherDelegate(const FilePathWatcher::Callback& callback)
+      : callback_(callback) {}
+
+  // FilePathWatcher::Delegate implementation.
+  virtual void OnFilePathChanged(const FilePath& path) OVERRIDE {
+    callback_.Run(path, false);
+  }
+
+  virtual void OnFilePathError(const FilePath& path) OVERRIDE {
+    callback_.Run(path, true);
+  }
+
+ private:
+  virtual ~FilePathWatcherDelegate() {}
+
+  FilePathWatcher::Callback callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherDelegate);
+};
+
+}  // namespace
+
 FilePathWatcher::~FilePathWatcher() {
   impl_->Cancel();
 }
@@ -35,5 +62,9 @@ FilePathWatcher::PlatformDelegate::~PlatformDelegate() {
   DCHECK(is_cancelled());
 }
 
+bool FilePathWatcher::Watch(const FilePath& path, const Callback& callback) {
+  return Watch(path, new FilePathWatcherDelegate(callback));
+}
+
 }  // namespace files
 }  // namespace base