Extend password export/import flags to Android

The connected base::Features are also used on Android, but the
about:flags page is set up to only allow changing it on desktop.

This CL adds the possibility to control those two base::Features
through about:flags on Android as well.

Bug: 788701
Change-Id: Ib6ae924ed453c8ceda746746fb10659d718d18e0
Reviewed-on: https://chromium-review.googlesource.com/808105Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521662}

chrome/browser/about_flags.cc

@@ -2614,12 +2614,10 @@ const FeatureEntry kFeatureEntries[] = {
      FEATURE_VALUE_TYPE(
          password_manager::features::kProtectSyncCredentialOnReauth)},
     {"password-export", flag_descriptions::kPasswordExportName,
-     flag_descriptions::kPasswordExportDescription,
-     kOsWin | kOsMac | kOsCrOS | kOsLinux,
+     flag_descriptions::kPasswordExportDescription, kOsAll,
      FEATURE_VALUE_TYPE(password_manager::features::kPasswordExport)},
     {"password-import", flag_descriptions::kPasswordImportName,
-     flag_descriptions::kPasswordImportDescription,
-     kOsWin | kOsMac | kOsCrOS | kOsLinux,
+     flag_descriptions::kPasswordImportDescription, kOsAll,
      FEATURE_VALUE_TYPE(password_manager::features::kPasswordImport)},
 #if defined(OS_CHROMEOS)
     {"enable-experimental-accessibility-features",