Adds a field trial to control Web API kill switches.

chrome/browser/permissions/permission_context_base.h

Index: chrome/browser/permissions/permission_context_base.h
diff --git a/chrome/browser/permissions/permission_context_base.h b/chrome/browser/permissions/permission_context_base.h
index 440880b957d9a3d30d8f65c321d79fbea0e53921..101a4ef82547caf9074451271cf2c1f3de02cecd 100644
--- a/chrome/browser/permissions/permission_context_base.h
+++ b/chrome/browser/permissions/permission_context_base.h
@@ -127,6 +127,9 @@ class PermissionContextBase : public KeyedService {
   // Whether the permission should be restricted to secure origins.
   virtual bool IsRestrictedToSecureOrigins() const = 0;
 
+  // Whether the kill switch has been enabled for this API.
+  virtual bool IsApiKillSwitchOn() const;
+
  private:
   // Called when a bubble is no longer used so it can be cleaned up.
   void CleanUpBubble(const PermissionRequestID& id);