docs: Change "ChromeOS" to "Chrome OS".

docs/adding_to_third_party.md

 # Adding third_party Libraries
 
 [TOC]
 
 Using third party code can save time and is consistent with our values - no need
 to reinvent the wheel! We put all code that isn't written by Chromium developers
 into src/third_party (even if you end up modifying just a few functions). We do
 this to make it easy to track license compliance, security patches, and supply
 the right credit and attributions. It also makes it a lot easier for other
 projects that embed our code to track what is Chromium licensed and what is
@@ skipping 64 matching lines @@
 See the ["Odds n' Ends"](adding_to_third_party.md#Odds-n_Ends) Section below if
 you run into any failures running these.
 
 If the library will never be shipped as a part of Chrome (e.g. build-time tools,
 testing tools), make sure to set "License File" as "NOT_SHIPPED" so that the
 license is not included in about:credits page.
 
 ### Modify DEPS
 
 If the code is applicable and will be compiled on all supported Chromium
-platforms (Windows, Mac, Linux, ChromeOS, iOS, Android), check it in to
+platforms (Windows, Mac, Linux, Chrome OS, iOS, Android), check it in to
 [src/third_party](http://src.chromium.org/viewvc/chrome/trunk/src/third_party/). 
 
 If the code is only applicable to certain platforms, check it in to
 [src/third_party](http://src.chromium.org/viewvc/chrome/trunk/src/third_party/)
 and add an entry to the
 [DEPS](http://src.chromium.org/viewvc/chrome/trunk/src/DEPS) file that causes
 the code to be checked out from src/third_party into src/third_party by gclient.
 
 _Explanation: Checking it into src/third_party causes all developers to need to
 check out your code. This wastes disk space cause syncing to take longer for
@@ skipping 97 matching lines @@
 
 * Missing license file
     * Make sure that the license file is present. It should be called 'LICENSE',
       or otherwise README.chromium file must point to it explicitly.
 * The following files contain a third-party license but are not in a listed
   third-party directory...
     * Check if it's a false positive (e.g. 'copyright' word used in a string
       literal), if so, update
       [src/tools/copyright_scanner/third_party_files_whitelist.txt](https://code.google.com/p/chromium/codesearch#chromium/src/tools/copyright_scanner/third_party_files_whitelist.txt)
       file. Otherwise, please move the code into third_party.