Fix few trivial Coverity issues, mainly PASS_BY_VALUE.

base/file_path.cc

 // Copyright (c) 2008 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.
 
 #include "base/file_path.h"
 #include "base/logging.h"
 
 // These includes are just for the *Hack functions, and should be removed
 // when those functions are removed.
 #include "base/string_piece.h"
@@ skipping 65 matching lines @@
   }
   // Look for a pair of leading separators.
   return path.length() > 1 &&
       FilePath::IsSeparator(path[0]) && FilePath::IsSeparator(path[1]);
 #else  // FILE_PATH_USES_DRIVE_LETTERS
   // Look for a separator in the first position.
   return path.length() > 0 && FilePath::IsSeparator(path[0]);
 #endif  // FILE_PATH_USES_DRIVE_LETTERS
 }
 
-bool AreAllSeparators(FilePath::StringType input) {
+bool AreAllSeparators(const FilePath::StringType& input) {
   for (FilePath::StringType::const_iterator it = input.begin();
       it != input.end(); ++it) {
     if (!FilePath::IsSeparator(*it))
       return false;
   }
 
   return true;
 }
 
 }  // namespace
@@ skipping 348 matching lines @@
        --pos) {
     // If the string only has two separators and they're at the beginning,
     // don't strip them, unless the string began with more than two separators.
     if (pos != start + 1 || last_stripped == start + 2 ||
         !IsSeparator(path_[start - 1])) {
       path_.resize(pos - 1);
       last_stripped = pos;
     }
   }
 }