Fix third_party/tcmalloc/vendor/README_windows.txt line endings.

Was committed as CRLF line endings in r576221, despite existing rule
against this, which caused git to always consider this file to be dirty.

Converted to Unix (LF) line endings.

Bug: 866342
Change-Id: Ie05d8a83e7ef6721bb0dd58fe3e278da245c313c
Reviewed-on: https://chromium-review.googlesource.com/1146407Reviewed-by: Primiano Tucci <primiano@chromium.org>
Commit-Queue: Matt Giuca <mgiuca@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577333}

third_party/tcmalloc/README.chromium

@@ -114,3 +114,4 @@ Modifications:
 - Added support for mips64el.
 - Pulled SuggestedDelayNS() implementation for 32bit architectures which do not support 64bit atomicity
 - Pulled several mipsel related changes from lss project to fix compile errors
+- Fixed line endings in vendor/README_windows.txt to Unix (LF)