Bug 887334 - Stop setting the compartment to defaultCompartmentObject_->compartment(). r=luke

With this change, defaultCompartmentObject_ is just an opaque (though traced)
piece of embedder state on the cx.

dom/base/nsGlobalWindow.cpp

@@ -2082,8 +2082,7 @@ nsGlobalWindow::SetOuterObject(JSContext* aCx, JS::Handle<JSObject*> aOuterObjec
 {
   JSAutoCompartment ac(aCx, aOuterObject);
 
-  // Force our context's global object to be the outer.
-  // NB: JS_SetGlobalObject sets aCx->compartment.
+  // Indicate the default compartment object associated with this cx.
   JS_SetGlobalObject(aCx, aOuterObject);
 
   // Set up the prototype for the outer object.

js/src/jscntxt.cpp

@@ -1138,14 +1138,9 @@ JSContext::saveFrameChain()
     if (Activation *act = mainThread().activation())
         act->saveFrameChain();
 
-    if (defaultCompartmentObject_)
-        setCompartment(defaultCompartmentObject_->compartment());
-    else
-        setCompartment(NULL);
+    setCompartment(NULL);
     enterCompartmentDepth_ = 0;
 
-    if (isExceptionPending())
-        wrapPendingException();
     return true;
 }
 

js/src/jscntxtinlines.h

@@ -401,19 +401,6 @@ inline void
 JSContext::setDefaultCompartmentObject(JSObject *obj)
 {
     defaultCompartmentObject_ = obj;
-
-    if (!hasEnteredCompartment()) {
-        /*
-         * If JSAPI callers want to JS_SetGlobalObject while code is running,
-         * they must have entered a compartment (otherwise there will be no
-         * final leaveCompartment call to set the context's compartment back to
-         * defaultCompartmentObject->compartment()).
-         */
-        JS_ASSERT(!currentlyRunning());
-        setCompartment(obj ? obj->compartment() : NULL);
-        if (throwing)
-            wrapPendingException();
-    }
 }
 
 inline void
@@ -440,21 +427,9 @@ JSContext::leaveCompartment(JSCompartment *oldCompartment)
     enterCompartmentDepth_--;
 
     compartment()->leave();
+    setCompartment(oldCompartment);
 
-    /*
-     * Before we entered the current compartment, 'compartment' was
-     * 'oldCompartment', so we might want to simply set it back. However, we
-     * currently have this terrible scheme whereby defaultCompartmentObject_ can
-     * be updated while enterCompartmentDepth_ > 0. In this case, oldCompartment
-     * != defaultCompartmentObject_->compartment and we must ignore
-     * oldCompartment.
-     */
-    if (hasEnteredCompartment() || !defaultCompartmentObject_)
-        setCompartment(oldCompartment);
-    else
-        setCompartment(defaultCompartmentObject_->compartment());
-
-    if (throwing)
+    if (throwing && oldCompartment)
         wrapPendingException();
 }