Adds a field trial to control Web API kill switches.

chrome/browser/permissions/permission_context_base.cc

Index: chrome/browser/permissions/permission_context_base.cc
diff --git a/chrome/browser/permissions/permission_context_base.cc b/chrome/browser/permissions/permission_context_base.cc
index f329b2bbb640a9b6826ee85bac39ff266dbc7528..c3b8257e219134321a14a246d39077efba66acf2 100644
--- a/chrome/browser/permissions/permission_context_base.cc
+++ b/chrome/browser/permissions/permission_context_base.cc
@@ -16,10 +16,15 @@
 #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)
@@ -42,6 +47,15 @@ void PermissionContextBase::RequestPermission(
     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(),
@@ -53,6 +67,11 @@ void PermissionContextBase::RequestPermission(
 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;
@@ -256,3 +275,11 @@ void PermissionContextBase::UpdateContentSetting(
       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;
+}