Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /content/browser/font_unique_name_lookup

This CL was uploaded by git cl split.

R=drott@chromium.org

Bug: 1110266
Change-Id: I6e746e1ed90bf2bab026c0c159ebd926d7411979
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371289
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801012}

content/browser/font_unique_name_lookup/font_unique_name_browsertest.cc

@@ -65,7 +65,7 @@ const char* kExpectedFontFamilyNames[] = {"AndroidClock",
                                           "Roboto Condensed",
                                           "Roboto Condensed",
                                           "Roboto"};
-#elif defined(OS_LINUX)
+#elif defined(OS_LINUX) || defined(OS_CHROMEOS)
 const char* kExpectedFontFamilyNames[] = {"Ahem",
                                           "Arimo",
                                           "Arimo",