Add a refresh button for providers which do not support watchers.

chrome/browser/chromeos/file_manager/volume_manager.h

Index: chrome/browser/chromeos/file_manager/volume_manager.h
diff --git a/chrome/browser/chromeos/file_manager/volume_manager.h b/chrome/browser/chromeos/file_manager/volume_manager.h
index 81166f4f5def4c297f7c3cd2bf796e4daa2a6d5d..33e05542354ad223bf52d3c8436813b5a6961b13 100644
--- a/chrome/browser/chromeos/file_manager/volume_manager.h
+++ b/chrome/browser/chromeos/file_manager/volume_manager.h
@@ -119,6 +119,7 @@ class Volume : public base::SupportsWeakPtr<Volume> {
   bool is_read_only() const { return is_read_only_; }
   bool has_media() const { return has_media_; }
   bool configurable() const { return configurable_; }
+  bool watchable() const { return watchable_; }
 
  private:
   Volume();
@@ -183,6 +184,9 @@ class Volume : public base::SupportsWeakPtr<Volume> {
   // True if the volume is configurable.
   bool configurable_;
 
+  // True if the volume notifies about changes via file/directory watchers.
+  bool watchable_;
+
   DISALLOW_COPY_AND_ASSIGN(Volume);
 };