[fsp] Add support for truncating files.

chrome/browser/chromeos/file_system_provider/provided_file_system.cc

Index: chrome/browser/chromeos/file_system_provider/provided_file_system.cc
diff --git a/chrome/browser/chromeos/file_system_provider/provided_file_system.cc b/chrome/browser/chromeos/file_system_provider/provided_file_system.cc
index 479494e008a7ee587e8d010dc576f48b99cda311..da0b7d0a8ba47df97cc8c5708fe8f2fbbd61bdf4 100644
--- a/chrome/browser/chromeos/file_system_provider/provided_file_system.cc
+++ b/chrome/browser/chromeos/file_system_provider/provided_file_system.cc
@@ -17,6 +17,7 @@
 #include "chrome/browser/chromeos/file_system_provider/operations/open_file.h"
 #include "chrome/browser/chromeos/file_system_provider/operations/read_directory.h"
 #include "chrome/browser/chromeos/file_system_provider/operations/read_file.h"
+#include "chrome/browser/chromeos/file_system_provider/operations/truncate.h"
 #include "chrome/browser/chromeos/file_system_provider/operations/unmount.h"
 #include "chrome/browser/chromeos/file_system_provider/request_manager.h"
 #include "chrome/browser/profiles/profile.h"
@@ -213,6 +214,22 @@ void ProvidedFileSystem::MoveEntry(
   }
 }
 
+void ProvidedFileSystem::Truncate(
+    const base::FilePath& file_path,
+    int64 length,
+    const fileapi::AsyncFileUtil::StatusCallback& callback) {
+  if (!request_manager_.CreateRequest(
+          TRUNCATE,
+          scoped_ptr<RequestManager::HandlerInterface>(
+              new operations::Truncate(event_router_,
+                                       file_system_info_,
+                                       file_path,
+                                       length,
+                                       callback)))) {
+    callback.Run(base::File::FILE_ERROR_SECURITY);
+  }
+}
+
 const ProvidedFileSystemInfo& ProvidedFileSystem::GetFileSystemInfo() const {
   return file_system_info_;
 }