Fix bug with StreamController sync

StreamControllers used to fire synchronously but now have an optional
sync property in the constructor. Must only use sync StreamControllers
for our events.

Author: marcojakob

lib/html5_dnd.dart

@@ -111,9 +111,9 @@ class Draggable {
   // -------------------
   // Private
   // -------------------
-  StreamController<DraggableEvent> _onDragStart = new StreamController<DraggableEvent>();
-  StreamController<DraggableEvent> _onDrag = new StreamController<DraggableEvent>();
-  StreamController<DraggableEvent> _onDragEnd = new StreamController<DraggableEvent>();
+  StreamController<DraggableEvent> _onDragStart = new StreamController<DraggableEvent>(sync: true);
+  StreamController<DraggableEvent> _onDrag = new StreamController<DraggableEvent>(sync: true);
+  StreamController<DraggableEvent> _onDragEnd = new StreamController<DraggableEvent>(sync: true);
 
   /**
    * Creates a draggable with the specified [element].
@@ -366,10 +366,10 @@ class Dropzone {
   // ----------
   // Events
   // ----------
-  StreamController<DropzoneEvent> _onDragEnter = new StreamController<DropzoneEvent>();
-  StreamController<DropzoneEvent> _onDragOver = new StreamController<DropzoneEvent>();
-  StreamController<DropzoneEvent> _onDragLeave = new StreamController<DropzoneEvent>();
-  StreamController<DropzoneEvent> _onDrop = new StreamController<DropzoneEvent>();
+  StreamController<DropzoneEvent> _onDragEnter = new StreamController<DropzoneEvent>(sync: true);
+  StreamController<DropzoneEvent> _onDragOver = new StreamController<DropzoneEvent>(sync: true);
+  StreamController<DropzoneEvent> _onDragLeave = new StreamController<DropzoneEvent>(sync: true);
+  StreamController<DropzoneEvent> _onDrop = new StreamController<DropzoneEvent>(sync: true);
 
   /**
    * Fired when the mouse is first moved over this dropzone while dragging the 

lib/html5_sortable.dart

@@ -72,7 +72,7 @@ class Sortable {
   /// Callback function that is called when the drag is ended by a drop.
   /// If the user aborted the drag, the function is not called.
   StreamController<SortableResult> _onSortableComplete = 
-      new StreamController<SortableResult>();
+      new StreamController<SortableResult>(sync: true);
 
   static final RegExp _floatRegExp = new RegExp(r'left|right');
 
@@ -114,6 +114,7 @@ class Sortable {
       _placeholder = new _Placeholder(event.draggable.element, placeholderClass, 
           forcePlaceholderSize);
       _placeholder.onDrop.listen((_) {
+        _dropped = true;
         _showDraggable(_placeholder.placeholderPosition);
       });
     })
@@ -124,6 +125,7 @@ class Sortable {
         // Not dropped. This means the drag ended outside of a placeholder or
         // the drag was cancelled somehow (ESC-key, ...)
         // Revert to state before dragging.
+        _logger.finest('onDragEnd not dropped -> Revert to state before dragging');
         _showDraggable(_originalPosition);
       }
 
@@ -172,17 +174,9 @@ class Sortable {
         }
       }
     });
-    
-    dropzone.onDrop.listen((DropzoneEvent event) {
-      // Return if drag is not from this sortable.
-      if (_placeholder == null) return;
-      _logger.finest('dropzone onDrop');
-      _showDraggable(_placeholder.placeholderPosition);
-    });
   }
 
   void _showDraggable(Position newPosition) {
-    _dropped = true;
     _placeholder.placeholderElement.remove();
     newPosition.insert(currentDraggable.element);
 
@@ -209,7 +203,8 @@ class _Placeholder {
   /// Fired when a drag element has been dropped in this placeholder.
   Stream<_Placeholder> get onDrop => _onDrop.stream;
 
-  StreamController<_Placeholder> _onDrop = new StreamController<_Placeholder>();
+  StreamController<_Placeholder> _onDrop = 
+      new StreamController<_Placeholder>(sync: true);
 
   /**
    * Creates a new placeholder for the specified [draggableElement].

lib/src/html5_utils.dart

@@ -50,9 +50,8 @@ bool get supportsSetDragImage {
       // Call via javascript function.
       _supportsSetDragImage = js.context.supportsSetDragImage();
     } on NoSuchMethodError {
-      _logger.severe('JavaScript method "supportsSetDragImage()" not found. Please' 
-          + ' load the file "dnd.polyfill.js" in your application html.');
-      _lazySupportsSetDragImage = false;
+      _logger.severe('JavaScript method "supportsSetDragImage()" not found. Please load the file "dnd.polyfill.js" in your application html.');
+      _supportsSetDragImage = false;
     } catch(e) {
       _logger.severe('Calling "supportsSetDragImage()" via JavaScript failed: ' 
           + e.toString());