Bug 1359245 - Keep a linked list of CycleCollectedJSContexts in the runtime (r=mccr8)

This patch keeps a list of all the cooperatively scheduled contexts that are
linked to a runtime. In places where we need to iterate over all contexts (for
GC, specifically), it iterates over the list.

MozReview-Commit-ID: 3pKJX78f2l0

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -562,6 +562,18 @@ CycleCollectedJSRuntime::~CycleCollectedJSRuntime()
   MOZ_ASSERT(!mDeferredFinalizerTable.Count());
 }
 
+void
+CycleCollectedJSRuntime::AddContext(CycleCollectedJSContext* aContext)
+{
+  mContexts.insertBack(aContext);
+}
+
+void
+CycleCollectedJSRuntime::RemoveContext(CycleCollectedJSContext* aContext)
+{
+  aContext->removeFrom(mContexts);
+}
+
 size_t
 CycleCollectedJSRuntime::SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
 {