[ios] Adds a buildflag for the ios_app_bundle_id_prefix.

ios/chrome/common/app_group/app_group_constants.mm

Index: ios/chrome/common/app_group/app_group_constants.mm
diff --git a/ios/chrome/common/app_group/app_group_constants.mm b/ios/chrome/common/app_group/app_group_constants.mm
index e5911ba6de99fbd1f7fcd63c9801388a5724d279..bc2863170d7cc4258c059e495d7cf4f3e089662c 100644
--- a/ios/chrome/common/app_group/app_group_constants.mm
+++ b/ios/chrome/common/app_group/app_group_constants.mm
@@ -6,17 +6,13 @@
 
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
+#include "build/config/ios/ios_app_bundle_id_prefix.h"
 #include "components/version_info/version_info.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
-namespace {
-NSString* const kChromeAppGroupIdentifier =
-    @"group." IOS_BUNDLE_ID_PREFIX ".chrome";
-}
-
 namespace app_group {
 
 const char kChromeAppGroupXCallbackCommand[] = "app-group-command";
@@ -51,7 +47,8 @@ NSString* ApplicationGroup() {
   NSBundle* bundle = [NSBundle mainBundle];
   NSString* group = [bundle objectForInfoDictionaryKey:@"KSApplicationGroup"];
   if (![group length]) {
-    return kChromeAppGroupIdentifier;
+    return [NSString stringWithFormat:@"group.%s.chrome",
+                                      BUILDFLAG(IOS_APP_BUNDLE_ID_PREFIX), nil];

[rohitrao (ping after 24h), 2016/12/13 14:14:30]

Is there a better way to concatenate these strings?

[sdefresne, 2016/12/13 15:18:02]

Ah, BUILDFLAG(IOS_APP_BUNDLE_ID_PREFIX) expands to ("org.chromium") and we
cannot use the concatenation from the preprocessor. That's lame.

I don't think there is a better way that stringWithFormat here. Should only
happens for non official builds though (since official sets KSApplicationGroup
IIRC).

   }
   return group;
 }