[ios] Add new Experimental Flag for an alternate Discover Server URL

This URL will be used to test Discover Feed server changes on a client.

Bug: 1169382
Change-Id: I3fa1d7ccdb380ecfd295985d771bc9a44acf793f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643094
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845878}

ios/chrome/browser/resources/Settings.bundle/Experimental.plist

@@ -4,6 +4,24 @@
 <dict>
 	<key>PreferenceSpecifiers</key>
 	<array>
+		<dict>
+			<key>Title</key>
+			<string>Discover Feed</string>
+			<key>Type</key>
+			<string>PSGroupSpecifier</string>
+		</dict>
+		<dict>
+			<key>Type</key>
+			<string>PSTextFieldSpecifier</string>
+			<key>Title</key>
+			<string>DiscoverFeed Server URL</string>
+			<key>Key</key>
+			<string>AlternateDiscoverFeedServerURL</string>
+			<key>DefaultValue</key>
+			<string></string>
+			<key>AutocorrectionType</key>
+			<string>No</string>
+		</dict>
 		<dict>
 			<key>Type</key>
 			<string>PSGroupSpecifier</string>

ios/chrome/browser/system_flags.h

@@ -44,6 +44,9 @@ std::string GetOriginServerHost();
 // If |WHATS_NEW_DEFAULT| is returned, no promo is force enabled.
 WhatsNewPromoStatus GetWhatsNewPromoStatus();
 
+// Returns the URL for the alternative Discover Feed server.
+std::string getAlternateDiscoverFeedServerURL();
+
 // Whether memory debugging tools are enabled.
 bool IsMemoryDebuggingEnabled();
 

ios/chrome/browser/system_flags.mm

@@ -33,6 +33,8 @@
 
 namespace {
 
+NSString* const kAlternateDiscoverFeedServerURL =
+    @"AlternateDiscoverFeedServerURL";
 NSString* const kDisableDCHECKCrashes = @"DisableDCHECKCrashes";
 NSString* const kEnableStartupCrash = @"EnableStartupCrash";
 NSString* const kFirstRunForceEnabled = @"FirstRunForceEnabled";
@@ -81,6 +83,12 @@ WhatsNewPromoStatus GetWhatsNewPromoStatus() {
   return static_cast<WhatsNewPromoStatus>(status);
 }
 
+std::string getAlternateDiscoverFeedServerURL() {
+  NSString* alternateServerURL = [[NSUserDefaults standardUserDefaults]
+      stringForKey:kAlternateDiscoverFeedServerURL];
+  return base::SysNSStringToUTF8(alternateServerURL);
+}
+
 bool IsMemoryDebuggingEnabled() {
 // Always return true for Chromium builds, but check the user default for
 // official builds because memory debugging should never be enabled on stable.