Only show the 'Enable Mash' flag on CrOS.

The string resources required for the 'Enable Mash' flag are only avabilable
on CrOS, so only add the flag on CrOS. Note we can assume that
ENABLE_PACKAGE_MASH_SERVICES is always enabled on CrOS.

[email protected],[email protected]

BUG=NONE

Review-Url: https://codereview.chromium.org/2694443002
Cr-Commit-Position: refs/heads/master@{#449760}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index df649b4..2860a91 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -930,11 +930,9 @@
      IDS_FLAGS_RUN_ALL_FLASH_IN_ALLOW_MODE_DESCRIPTION, kOsDesktop,
      FEATURE_VALUE_TYPE(features::kRunAllFlashInAllowMode)},
 #endif  // ENABLE_PLUGINS
-#if BUILDFLAG(ENABLE_PACKAGE_MASH_SERVICES)
+#if defined(OS_CHROMEOS)
     {"mash", IDS_FLAGS_USE_MASH_NAME, IDS_FLAGS_USE_MASH_DESCRIPTION, kOsCrOS,
      SINGLE_VALUE_TYPE(switches::kMash)},
-#endif  // BUILDFLAG(ENABLE_PACKAGE_MASH_SERVICES)
-#if defined(OS_CHROMEOS)
     {"allow-touchpad-three-finger-click",
      IDS_FLAGS_ALLOW_TOUCHPAD_THREE_FINGER_CLICK_NAME,
      IDS_FLAGS_ALLOW_TOUCHPAD_THREE_FINGER_CLICK_DESCRIPTION, kOsCrOS,