Fix the fix to 40406, fixing bustage.

Don't destroy the per-thread safe JS context on cleanup if that context was provided through the setter.

r=waterson

js/src/xpconnect/src/xpcprivate.h

@@ -1371,6 +1371,7 @@ private:
     nsDeque*          mJSContextStack;
     JSContext*        mSafeJSContext;
     xpcPerThreadData* mNextThread;
+    PRBool            mSafeContextIsFromSetter;
 
     static PRLock*           gLock;
     static xpcPerThreadData* gThreads;

js/src/xpconnect/src/xpcthreadcontext.cpp

@@ -198,7 +198,8 @@ xpcPerThreadData::xpcPerThreadData()
     :   mException(nsnull),
         mJSContextStack(new nsDeque(nsnull)),
         mSafeJSContext(nsnull),
-        mNextThread(nsnull)
+        mNextThread(nsnull),
+        mSafeContextIsFromSetter(PR_FALSE)
 {
     if(gLock)
     {
@@ -219,7 +220,7 @@ xpcPerThreadData::Cleanup()
         mJSContextStack = nsnull;
     }
 
-    if(mSafeJSContext)
+    if(mSafeJSContext && !mSafeContextIsFromSetter)
     {
         JS_DestroyContext(mSafeJSContext);
         mSafeJSContext = nsnull;
@@ -328,8 +329,8 @@ xpcPerThreadData::GetSafeJSContext()
 nsresult
 xpcPerThreadData::SetSafeJSContext(JSContext *cx)
 {
-    NS_ASSERTION(!mSafeJSContext, "SetSafeJSContext called too late!");
     mSafeJSContext = cx;
+    mSafeContextIsFromSetter = PR_TRUE;
     return NS_OK;
 }