Bug 1052052 - Convert AutoJSContext to AutoJSAPI. r=gabor

With this change, the only cx push left in the tree happens inside of AutoJSAPI. \o/

dom/base/ScriptSettings.cpp

@@ -465,8 +465,8 @@ AutoJSContext::Init(bool aSafe MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL)
   }
 
   if (!mCx) {
-    mCx = xpc->GetSafeJSContext();
-    mPusher.emplace(mCx);
+    mJSAPI.Init();
+    mCx = mJSAPI.cx();
   }
 }
 

dom/base/ScriptSettings.h

@@ -300,7 +300,7 @@ protected:
   void Init(bool aSafe MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
 
   JSContext* mCx;
-  Maybe<dom::danger::AutoCxPusher> mPusher;
+  dom::AutoJSAPI mJSAPI;
   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
 };