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 /chrome/test/chromedriver

This CL was uploaded by git cl split.

R=johnchen@chromium.org

Bug: 1110266
Change-Id: I0c88c4b894c196ddf5b5da65734ecdc8723f05e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370286
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800890}

chrome/test/chromedriver/key_converter_unittest.cc

@@ -277,7 +277,7 @@ TEST(KeyConverter, AllShorthandKeys) {
       ->Generate(&key_events);
   builder.Generate(&key_events);
   builder.SetKeyCode(ui::VKEY_TAB);
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
   builder.SetText("\t", "\t")->Generate(&key_events);
 #else
   builder.SetText(std::string(), std::string());
@@ -285,7 +285,7 @@ TEST(KeyConverter, AllShorthandKeys) {
   key_events.push_back(builder.SetType(kKeyUpEventType)->Build());
 #endif
   builder.SetKeyCode(ui::VKEY_BACK);
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
   builder.SetText("\b", "\b")->Generate(&key_events);
 #else
   builder.SetText(std::string(), std::string());
@@ -296,7 +296,7 @@ TEST(KeyConverter, AllShorthandKeys) {
   CheckEventsReleaseModifiers("\n\r\n\t\b ", key_events);
 }
 
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
 // Fails on bots: crbug.com/174962
 #define MAYBE_AllEnglishKeyboardSymbols DISABLED_AllEnglishKeyboardSymbols
 #else