Fixed IsolateNameServer documentation (flutter#6344)

We were using `//` instead of `///` so docs were not being generated.

lib/ui/isolate_name_server.dart

@@ -4,30 +4,31 @@
 
 part of dart.ui;
 
+/// Contains methods to allow for simple sharing of SendPorts across isolates.
 abstract class IsolateNameServer {
-  // Looks up the [SendPort] associated with a given name. Returns null
-  // if the name does not exist.
-  //
-  // `name` must not be null.
+  /// Looks up the [SendPort] associated with a given name. Returns null
+  /// if the name does not exist.
+  ///
+  /// `name` must not be null.
   static SendPort lookupPortByName(String name) {
     assert(name != null, "'name' cannot be null.");
     return _lookupPortByName(name);
   }
 
-  // Registers a SendPort with a given name. Returns true if registration is
-  // successful, false if the name entry already exists.
-  //
-  // `port` and `name` must not be null.
+  /// Registers a SendPort with a given name. Returns true if registration is
+  /// successful, false if the name entry already exists.
+  ///
+  /// `port` and `name` must not be null.
   static bool registerPortWithName(SendPort port, String name) {
     assert(port != null, "'port' cannot be null.");
     assert(name != null, "'name' cannot be null.");
     return _registerPortWithName(port, name);
   }
 
-  // Removes a name to SendPort mapping given a name. Returns true if the
-  // mapping was successfully removed, false if the mapping does not exist.
-  //
-  // `name` must not be null.
+  /// Removes a name to SendPort mapping given a name. Returns true if the
+  /// mapping was successfully removed, false if the mapping does not exist.
+  ///
+  /// `name` must not be null.
   static bool removePortNameMapping(String name) {
     assert(name != null, "'name' cannot be null.");
     return _removePortNameMapping(name);