Add about:flags entry for SyncStandaloneTransport on iOS

I added the same flag for other platforms in
https://chromium-review.googlesource.com/c/chromium/src/+/1161917, but
forgot about iOS :(

Bug: 856179
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: I4e5543b23f64fd31da196e5ea1394fabe71cef30
Reviewed-on: https://chromium-review.googlesource.com/1193282Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586638}

ios/chrome/browser/about_flags.mm

@@ -369,6 +369,10 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
     {"app-launcher-refresh", flag_descriptions::kAppLauncherRefreshName,
      flag_descriptions::kAppLauncherRefreshDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kAppLauncherRefresh)},
+    {"sync-standalone-transport",
+     flag_descriptions::kSyncStandaloneTransportName,
+     flag_descriptions::kSyncStandaloneTransportDescription, flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(switches::kSyncStandaloneTransport)},
 };
 
 // Add all switches from experimental flags to |command_line|.

ios/chrome/browser/ios_chrome_flag_descriptions.cc

@@ -44,6 +44,12 @@ const char kSyncSandboxName[] = "Use Chrome Sync sandbox";
 const char kSyncSandboxDescription[] =
     "Connects to the testing server for Chrome Sync.";
 
+const char kSyncStandaloneTransportName[] = "Allow Sync standalone transport";
+const char kSyncStandaloneTransportDescription[] =
+    "If enabled, allows Chrome Sync to start in standalone transport mode. In "
+    "this mode, the Sync machinery can start without user opt-in, but only a "
+    "subset of data types are supported.";
+
 const char kWalletServiceUseSandboxName[] = "Use Google Payments sandbox";
 const char kWalletServiceUseSandboxDescription[] =
     "Uses the sandbox service for Google Payments API calls.";

ios/chrome/browser/ios_chrome_flag_descriptions.h

@@ -35,6 +35,11 @@ extern const char
 extern const char kSyncSandboxName[];
 extern const char kSyncSandboxDescription[];
 
+// Title and description for the flag to control if Chrome Sync can start up in
+// standalone transport mode.
+extern const char kSyncStandaloneTransportName[];
+extern const char kSyncStandaloneTransportDescription[];
+
 // Title and description for the flag to control if Google Payments API calls
 // should use the sandbox servers.
 extern const char kWalletServiceUseSandboxName[];