Clean up most of the ChromeOS headers in non-ChromeOS build

chrome/browser/diagnostics/diagnostics_controller_unittest.cc

Index: chrome/browser/diagnostics/diagnostics_controller_unittest.cc
diff --git a/chrome/browser/diagnostics/diagnostics_controller_unittest.cc b/chrome/browser/diagnostics/diagnostics_controller_unittest.cc
index eb18d808a812cb5c490cbbd415f870992cf701fc..d004fb355bb316ea26b90415d465f78a23d53be9 100644
--- a/chrome/browser/diagnostics/diagnostics_controller_unittest.cc
+++ b/chrome/browser/diagnostics/diagnostics_controller_unittest.cc
@@ -18,9 +18,12 @@
 #include "chrome/browser/diagnostics/sqlite_diagnostics.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
-#include "chromeos/chromeos_constants.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if defined(OS_CHROMEOS)
+#include "chromeos/chromeos_constants.h"
+#endif  // defined(OS_CHROMEOS)
+
 namespace diagnostics {
 
 // Basic harness to acquire and release the required temporary environment to