Cleaning up usage of ChildAccountDetection experiment, replacing it with...

Cleaning up usage of ChildAccountDetection experiment, replacing it with target OS checks to enforce that the feature is always enabled on ChromeOS and Android, and disabled elsewhere

Bug: 795857
Change-Id: I2cd752637bc0cb5549606062c52c3b539d08677d
Reviewed-on: https://chromium-review.googlesource.com/1002972Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Rahul Chaturvedi <rkc@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Eduardo Cordeiro <escordeiro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550163}

chrome/browser/supervised_user/child_accounts/child_account_service.cc

@@ -37,10 +37,6 @@
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #endif
 
-#if !defined(OS_ANDROID)
-const char kChildAccountDetectionFieldTrialName[] = "ChildAccountDetection";
-#endif
-
 const char kGaiaCookieManagerSource[] = "child_account_service";
 
 // Normally, re-check the family info once per day.
@@ -90,15 +86,13 @@ ChildAccountService::~ChildAccountService() {
 
 // static
 bool ChildAccountService::IsChildAccountDetectionEnabled() {
-  // Child account detection is always enabled on Android.
-#if !defined(OS_ANDROID)
-  const std::string group_name =
-      base::FieldTrialList::FindFullName(kChildAccountDetectionFieldTrialName);
-  if (group_name == "Disabled")
-    return false;
-#endif
-
+// Child account detection is always enabled on Android and ChromeOS, and
+// disabled in other platforms.
+#if defined(OS_ANDROID) || defined(OS_CHROMEOS)
   return true;
+#else
+  return false;
+#endif
 }
 
 void ChildAccountService::RegisterProfilePrefs(

testing/variations/fieldtrial_testing_config.json

@@ -711,18 +711,6 @@
             ]
         }
     ],
-    "ChildAccountDetection": [
-        {
-            "platforms": [
-                "win"
-            ],
-            "experiments": [
-                {
-                    "name": "Disabled"
-                }
-            ]
-        }
-    ],
     "ChromeDashboard": [
         {
             "platforms": [