Bug 1282150 part 1. Add a mozilla::dom::danger::GetJSContext API. r=bholley

dom/base/ScriptSettings.cpp

@@ -7,6 +7,7 @@
 #include "mozilla/dom/ScriptSettings.h"
 #include "mozilla/ThreadLocal.h"
 #include "mozilla/Assertions.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
 
 #include "jsapi.h"
 #include "xpcpublic.h"
@@ -284,6 +285,14 @@ IsJSAPIActive()
   return topEntry && !topEntry->NoJSAPI();
 }
 
+namespace danger {
+JSContext*
+GetJSContext()
+{
+  return CycleCollectedJSRuntime::Get()->Context();
+}
+} // namespace danger
+
 AutoJSAPI::AutoJSAPI()
   : ScriptSettingsStackEntry(nullptr, eJSAPI)
   , mCx(nullptr)

dom/base/ScriptSettings.h

@@ -127,6 +127,15 @@ inline JSObject& IncumbentJSGlobal()
 // AutoJSAPI or AutoEntryScript to get yourself a properly set up JSContext.
 bool IsJSAPIActive();
 
+namespace danger {
+
+// Get the JSContext for this thread.  This is in the "danger" namespace because
+// we generally want people using AutoJSAPI instead, unless they really know
+// what they're doing.
+JSContext* GetJSContext();
+
+} // namespace danger
+
 class ScriptSettingsStack;
 class ScriptSettingsStackEntry {
   friend class ScriptSettingsStack;