Bug 1200063 - Add a generic implementation of nsITimerCallback that's usable with a lambda or other function object. r=kats

We can consider moving this to xpcom in the future.

gfx/layers/apz/util/APZThreadUtils.cpp

@@ -81,5 +81,7 @@ APZThreadUtils::RunOnControllerThread(Task* aTask)
 #endif
 }
 
+NS_IMPL_ISUPPORTS(GenericTimerCallbackBase, nsITimerCallback)
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/apz/util/APZThreadUtils.h

@@ -7,6 +7,7 @@
 #define mozilla_layers_APZThreadUtils_h
 
 #include "base/message_loop.h"
+#include "nsITimer.h"
 
 class Task;
 
@@ -51,6 +52,46 @@ public:
   static void RunOnControllerThread(Task* aTask);
 };
 
+// A base class for GenericTimerCallback<Function>.
+// This is necessary because NS_IMPL_ISUPPORTS doesn't work for a class
+// template.
+class GenericTimerCallbackBase : public nsITimerCallback
+{
+public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+protected:
+  virtual ~GenericTimerCallbackBase() {}
+};
+
+// An nsITimerCallback implementation that can be used with any function
+// object that's callable with no arguments.
+template <typename Function>
+class GenericTimerCallback final : public GenericTimerCallbackBase
+{
+public:
+  explicit GenericTimerCallback(const Function& aFunction) : mFunction(aFunction) {}
+
+  NS_IMETHODIMP Notify(nsITimer*) override
+  {
+    mFunction();
+    return NS_OK;
+  }
+private:
+  Function mFunction;
+};
+
+// Convenience function for constructing a GenericTimerCallback.
+// Returns a raw pointer, suitable for passing directly as an argument to
+// nsITimer::InitWithCallback(). The intention is to enable the following
+// terse inline usage:
+//    timer->InitWithCallback(NewTimerCallback([](){ ... }), delay);
+template <typename Function>
+GenericTimerCallback<Function>* NewTimerCallback(const Function& aFunction)
+{
+  return new GenericTimerCallback<Function>(aFunction);
+}
+
 } // namespace layers
 } // namespace mozilla