Adds a field trial to control Web API kill switches.

chrome/browser/permissions/permission_context_base.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/permissions/permission_context_base.h"
 
 #include "base/logging.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/content_settings/host_content_settings_map_factory.h"
 #include "chrome/browser/permissions/permission_bubble_request_impl.h"
 #include "chrome/browser/permissions/permission_context_uma_util.h"
 #include "chrome/browser/permissions/permission_queue_controller.h"
 #include "chrome/browser/permissions/permission_request_id.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/website_settings/permission_bubble_manager.h"
 #include "chrome/common/pref_names.h"
 #include "components/content_settings/core/browser/host_content_settings_map.h"
 #include "components/content_settings/core/browser/website_settings_registry.h"
+#include "components/variations/variations_associated_data.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/origin_util.h"
 
+// API kill switch Finch Trials
+static const char kApiFieldStudy[] = "ApiKillSwitch";
+static const char kApiFieldParamEnabledValue[] = "enabled";

[raymes, 2015/10/11 22:11:22]

Are these not defined as constants somewhere else?

[kcarattini, 2015/10/12 03:58:06]

No. From looking at other examples, these constants appear to be defined locally
where the field trial params are requested. The other place they would be
defined is in the actual finch trial config.

+
 PermissionContextBase::PermissionContextBase(
     Profile* profile,
     const ContentSettingsType permission_type)
     : profile_(profile),
       permission_type_(permission_type),
       weak_factory_(this) {
   permission_queue_controller_.reset(
       new PermissionQueueController(profile_, permission_type_));
 }
 
 PermissionContextBase::~PermissionContextBase() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 }
 
 void PermissionContextBase::RequestPermission(
     content::WebContents* web_contents,
     const PermissionRequestID& id,
     const GURL& requesting_frame,
     bool user_gesture,
     const BrowserPermissionCallback& callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
+  // First check if this API has been disabled through Finch.
+  if (IsApiKillSwitchOn()) {
+    // The kill switch is enabled for this API; Block all requests.
+    NotifyPermissionSet(id, requesting_frame.GetOrigin(),
+        web_contents->GetLastCommittedURL().GetOrigin(), callback,
+        false /* persist */, CONTENT_SETTING_BLOCK);
+    return;
+  }
+
   DecidePermission(web_contents,
                    id,
                    requesting_frame.GetOrigin(),
                    web_contents->GetLastCommittedURL().GetOrigin(),
                    user_gesture,
                    callback);
 }
 
 ContentSetting PermissionContextBase::GetPermissionStatus(
     const GURL& requesting_origin,
     const GURL& embedding_origin) const {
+
+  // If the API has been disabled through Finch, block all requests.
+  if (IsApiKillSwitchOn())
+    return CONTENT_SETTING_BLOCK;
+
   if (IsRestrictedToSecureOrigins() &&
       !content::IsOriginSecure(requesting_origin)) {
     return CONTENT_SETTING_BLOCK;
   }
 
   return HostContentSettingsMapFactory::GetForProfile(profile_)
       ->GetContentSetting(requesting_origin,
                           embedding_origin,
                           permission_type_,
                           std::string());
@@ skipping 183 matching lines @@
   DCHECK_EQ(requesting_origin, requesting_origin.GetOrigin());
   DCHECK_EQ(embedding_origin, embedding_origin.GetOrigin());
   DCHECK(content_setting == CONTENT_SETTING_ALLOW ||
          content_setting == CONTENT_SETTING_BLOCK);
 
   HostContentSettingsMapFactory::GetForProfile(profile_)->SetContentSetting(
       ContentSettingsPattern::FromURLNoWildcard(requesting_origin),
       ContentSettingsPattern::FromURLNoWildcard(embedding_origin),
       permission_type_, std::string(), content_setting);
 }
+
+bool PermissionContextBase::IsApiKillSwitchOn() const {

[raymes, 2015/10/11 22:11:22]

Should we add an about:flag to gate this behavior here too?

[kcarattini, 2015/10/12 03:58:06]

There is a way to force the field trial already with a commandline flag. If you
were referring to using a different flag, wouldn't that defeat the purpose of
being able to role out the kill switch quickly with a finch trial? I might have
misunderstood what you meant.

+  const std::string param =
+      variations::GetVariationParamValue(kApiFieldStudy,
+          PermissionContextUmaUtil::GetPermissionString(permission_type_));
+
+  return param == kApiFieldParamEnabledValue;
+}