Update ICU to 58 part1

* Note that this CL will be followed by CLs with local changes.
  Until then, ICU should not be rolled in DEPS. See READ_THIS_FIRST
  for details.

* Adjust scripts/update.sh and scripts/data_files_to_preserve.txt
  - CLDR/ICU added ckb/ast locale data. Drop them from the list to preserve.
  - source/layout does not exist in 58.1 any more.

* Update the tree to ICU 58.1 from the upstream by running
  scripts/update.sh

* Update README.chromium and add READ_THIS_FIRST to warn about the
  status of the tree.

BUG=637001
TEST=None
diff --git a/source/common/messagepattern.cpp b/source/common/messagepattern.cpp
index de0410b..31d5bb7 100644
--- a/source/common/messagepattern.cpp
+++ b/source/common/messagepattern.cpp
@@ -1,3 +1,5 @@
+// Copyright (C) 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
 /*
 *******************************************************************************
 *   Copyright (C) 2011-2012, International Business Machines
@@ -114,7 +116,7 @@
             errorCode=U_MEMORY_ALLOCATION_ERROR;
             return;
         }
-        uprv_memcpy(a.getAlias(), other.a.getAlias(), length*sizeof(T));
+        uprv_memcpy(a.getAlias(), other.a.getAlias(), (size_t)length*sizeof(T));
     }
 }