Bug 767938 part 5. Stop using the JSContext stack to get the current JSContext. r=bholley

dom/base/ScriptSettings.cpp

@@ -266,6 +266,13 @@ GetWebIDLCallerPrincipal()
   return aes->mWebIDLCallerPrincipal;
 }
 
+bool
+IsJSAPIActive()
+{
+  ScriptSettingsStackEntry* topEntry = ScriptSettingsStack::Top();
+  return topEntry && !topEntry->NoJSAPI();
+}
+
 AutoJSAPI::AutoJSAPI()
   : ScriptSettingsStackEntry(nullptr, eJSAPI)
   , mCx(nullptr)
@@ -796,13 +803,13 @@ AutoJSContext::AutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL)
 {
   JS::AutoSuppressGCAnalysis nogc;
   MOZ_ASSERT(!mCx, "mCx should not be initialized!");
+  MOZ_ASSERT(NS_IsMainThread());
 
   MOZ_GUARD_OBJECT_NOTIFIER_INIT;
 
-  nsXPConnect *xpc = nsXPConnect::XPConnect();
-  mCx = xpc->GetCurrentJSContext();
-
-  if (!mCx) {
+  if (IsJSAPIActive()) {
+    mCx = nsContentUtils::GetSafeJSContext();
+  } else {
     mJSAPI.Init();
     mCx = mJSAPI.cx();
   }

dom/base/ScriptSettings.h

@@ -150,6 +150,11 @@ inline JSObject& IncumbentJSGlobal()
   return *GetIncumbentGlobal()->GetGlobalJSObject();
 }
 
+// Returns whether JSAPI is active right now.  If it is not, working with a
+// JSContext you grab from somewhere random is not OK and you should be doing
+// AutoJSAPI or AutoEntryScript to get yourself a properly set up JSContext.
+bool IsJSAPIActive();
+
 class ScriptSettingsStack;
 class ScriptSettingsStackEntry {
   friend class ScriptSettingsStack;

dom/base/nsContentUtils.cpp

@@ -5469,7 +5469,10 @@ nsContentUtils::GetCurrentJSContext()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(IsInitialized());
-  return sXPConnect->GetCurrentJSContext();
+  if (!IsJSAPIActive()) {
+    return nullptr;
+  }
+  return GetSafeJSContext();
 }
 
 /* static */