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 761b489994bc1507925059216dd6746781d0402b..9367f916e36b9187b62e1ca90669e045e7e1ea1f 100644
--- a/chrome/browser/permissions/permission_context_base.cc
+++ b/chrome/browser/permissions/permission_context_base.cc
@@ -9,10 +9,12 @@
 #include "chrome/browser/content_settings/host_content_settings_map_factory.h"
 #include "chrome/browser/permissions/permission_context_uma_util.h"
 #include "chrome/browser/permissions/permission_request_id.h"
+#include "chrome/browser/permissions/permission_util.h"
 #include "chrome/browser/profiles/profile.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"
@@ -24,6 +26,13 @@
 #include "chrome/browser/ui/website_settings/permission_bubble_manager.h"
 #endif
 
+// static
+const char PermissionContextBase::kPermissionsKillSwitchFieldStudy[] =
+    "PermissionsKillSwitch";
+// static
+const char PermissionContextBase::kPermissionsKillSwitchBlockedValue[] =
+    "blocked";
+
 PermissionContextBase::PermissionContextBase(
     Profile* profile,
     const ContentSettingsType permission_type)
@@ -48,6 +57,15 @@ void PermissionContextBase::RequestPermission(
     const BrowserPermissionCallback& callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
+  // First check if this permission has been disabled.
+  if (IsPermissionKillSwitchOn()) {
+    // The kill switch is enabled for this permission; 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(),
@@ -59,6 +77,11 @@ void PermissionContextBase::RequestPermission(
 ContentSetting PermissionContextBase::GetPermissionStatus(
     const GURL& requesting_origin,
     const GURL& embedding_origin) const {
+
+  // If the permission has been disabled through Finch, block all requests.
+  if (IsPermissionKillSwitchOn())
+    return CONTENT_SETTING_BLOCK;
+
   if (IsRestrictedToSecureOrigins() &&
       !content::IsOriginSecure(requesting_origin)) {
     return CONTENT_SETTING_BLOCK;
@@ -262,3 +285,11 @@ void PermissionContextBase::UpdateContentSetting(
       ContentSettingsPattern::FromURLNoWildcard(embedding_origin),
       permission_type_, std::string(), content_setting);
 }
+
+bool PermissionContextBase::IsPermissionKillSwitchOn() const {
+  const std::string param =
+      variations::GetVariationParamValue(kPermissionsKillSwitchFieldStudy,
+          PermissionUtil::GetPermissionString(permission_type_));
+
+  return param == kPermissionsKillSwitchBlockedValue;
+}