Adds ScopedHandleBase::From

mojo/public/cpp/system/core.h

Index: mojo/public/cpp/system/core.h
diff --git a/mojo/public/cpp/system/core.h b/mojo/public/cpp/system/core.h
index 70221107ab0a2d6ee332d461294840c34c601d55..c786453863e9768a8f95b1d5413204c6af656c40 100644
--- a/mojo/public/cpp/system/core.h
+++ b/mojo/public/cpp/system/core.h
@@ -49,6 +49,12 @@ class ScopedHandleBase {
 
   const HandleType& get() const { return handle_; }
 
+  template <typename Passed>

[viettrungluu, 2014/04/03 20:42:48]

Nit: Could you call this PassedHandleType?

+  static ScopedHandleBase<HandleType> From(ScopedHandleBase<Passed> other) {
+    return ScopedHandleBase<HandleType>(

[viettrungluu, 2014/04/03 20:42:48]

Please add a comment:
// The |static_cast| here is needed to ensure type-safety (namely,
// that |HandleType| is a |PassedHandleType|).

+        static_cast<HandleType>(other.release().value()));

[viettrungluu, 2014/04/03 20:42:48]

It should be static_cast<HandleType>(other.release()).value()

+  }
+
   void swap(ScopedHandleBase& other) {
     handle_.swap(other.handle_);
   }