There should be a single entry point for creating IsolateHandle (#361)

src/global.rs

@@ -59,7 +59,7 @@ impl<T> Global<T> {
     Self {
       value: other_value
         .map(|v| unsafe { transmute(v8__Global__New(isolate, transmute(v))) }),
-      isolate_handle: other_value.map(|_| IsolateHandle::new(isolate)),
+      isolate_handle: other_value.map(|_| isolate.thread_safe_handle()),
     }
   }
 
@@ -104,7 +104,7 @@ impl<T> Global<T> {
         )
       },
     }
-    self.isolate_handle = other_value.map(|_| IsolateHandle::new(isolate));
+    self.isolate_handle = other_value.map(|_| isolate.thread_safe_handle());
   }
 
   /// If non-empty, destroy the underlying storage cell

src/isolate.rs

@@ -431,6 +431,12 @@ impl IsolateAnnex {
   }
 }
 
+/// IsolateHandle is a thread-safe reference to an Isolate. It's main use is to
+/// terminate execution of a running isolate from another thread.
+///
+/// It is created with Isolate::thread_safe_handle().
+///
+/// IsolateHandle is Cloneable, Send, and Sync.
 #[derive(Clone)]
 pub struct IsolateHandle(Arc<IsolateAnnex>);
 
@@ -445,7 +451,7 @@ impl IsolateHandle {
     self.0.isolate
   }
 
-  pub(crate) fn new(isolate: &mut Isolate) -> Self {
+  fn new(isolate: &mut Isolate) -> Self {
     Self(isolate.get_annex_arc())
   }