base: Move MemoryMappedFile out of file_util.h and into its own header file.

chrome/installer/util/move_tree_work_item_unittest.cc

Index: chrome/installer/util/move_tree_work_item_unittest.cc
diff --git a/chrome/installer/util/move_tree_work_item_unittest.cc b/chrome/installer/util/move_tree_work_item_unittest.cc
index bead46ebfc1cc517dfde18aee867746b3fb42e01..47b2729c7ac5f9d55e812288d13f0a027f02dd9c 100644
--- a/chrome/installer/util/move_tree_work_item_unittest.cc
+++ b/chrome/installer/util/move_tree_work_item_unittest.cc
@@ -8,6 +8,7 @@
 
 #include "base/base_paths.h"
 #include "base/file_util.h"
+#include "base/files/memory_mapped_file.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/path_service.h"
 #include "base/process_util.h"
@@ -412,7 +413,7 @@ TEST_F(MoveTreeWorkItemTest, MoveDirectoryDestExistsCheckForDuplicatesFull) {
   // Lock one of the files in the to destination directory to prevent moves.
   base::FilePath orig_to_file(
       to_dir.AppendASCII("From_Dir2").AppendASCII("From_File"));
-  file_util::MemoryMappedFile mapped_file;
+  base::MemoryMappedFile mapped_file;
   EXPECT_TRUE(mapped_file.Initialize(orig_to_file));
 
   // First check that we can't do the regular Move().