Exclude Android and iOS from file scheme elision

Android and iOS don't have the File security chip, and therefore still need to show
the file scheme. (Follow-up from https://chromium-review.googlesource.com/c/chromium/src/+/1274985.)

Bug: 818528
Change-Id: Ib42601f637a513d21c965bcbd48f8c66fcc5cc99
Reviewed-on: https://chromium-review.googlesource.com/c/1308077
Commit-Queue: Livvie Lin <livvielin@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604037}

components/omnibox/browser/omnibox_field_trial.cc

@@ -36,8 +36,16 @@ namespace omnibox {
 
 // Feature used to hide the scheme from steady state URLs displayed in the
 // toolbar. It is restored during editing.
-const base::Feature kHideFileUrlScheme{"OmniboxUIExperimentHideFileUrlScheme",
-                                       base::FEATURE_ENABLED_BY_DEFAULT};
+const base::Feature kHideFileUrlScheme {
+  "OmniboxUIExperimentHideFileUrlScheme",
+// Android and iOS don't have the File security chip, and therefore still
+// need to show the file scheme.
+#if defined(OS_ANDROID) || defined(OS_IOS)
+      base::FEATURE_DISABLED_BY_DEFAULT
+#else
+      base::FEATURE_ENABLED_BY_DEFAULT
+#endif
+};
 
 // Feature used to hide the scheme from steady state URLs displayed in the
 // toolbar. It is restored during editing.