Scroll exactly as we did before tiling

Except that now we store the scrolling tile, instead of the scrolling
row.

src/text-editor-component.coffee

@@ -354,6 +354,7 @@ class TextEditorComponent
       event.preventDefault() unless previousScrollLeft is @presenter.getScrollLeft()
     else
       # Scrolling vertically
+      @presenter.setScrollingTileId(@tileIdForNode(event.target))
       previousScrollTop = @presenter.getScrollTop()
       @presenter.setScrollTop(previousScrollTop - Math.round(wheelDeltaY * @scrollSensitivity))
       event.preventDefault() unless previousScrollTop is @presenter.getScrollTop()
@@ -728,11 +729,12 @@ class TextEditorComponent
 
   lineNumberNodeForScreenRow: (screenRow) -> @gutterContainerComponent.getLineNumberGutterComponent().lineNumberNodeForScreenRow(screenRow)
 
-  screenRowForNode: (node) ->
+  tileIdForNode: (node) ->
     while node?
-      if screenRow = node.dataset.screenRow
-        return parseInt(screenRow)
+      if tileId = node.dataset.tileId
+        return tileId
       node = node.parentElement
+
     null
 
   getFontSize: ->

src/text-editor-presenter.coffee

@@ -905,7 +905,7 @@ class TextEditorPresenter
 
       @emitDidUpdateState()
 
-  setScrollingTile: (tileId) ->
+  setScrollingTileId: (tileId) ->
     if @scrollingTile isnt tileId
       @scrollingTile = tileId
       @didStartScrolling()

src/tile-component.coffee

@@ -21,14 +21,11 @@ class TileComponent
     @screenRowsByLineId = {}
     @lineIdsByScreenRow = {}
     @domNode ?= document.createElement("div")
-    @domNode.addEventListener("mousewheel", @onMouseWheel)
+    @domNode.dataset.tileId = @id
     @domNode.style.position = "absolute"
     @domNode.style.display = "block"
     @domNode.classList.add("tile")
 
-  onMouseWheel: =>
-    @presenter.setScrollingTile(@id)
-
   getDomNode: ->
     @domNode