Respect horizontal scrollbar when rendering the vertical, and vice versa

We set overflow to hidden in the opposite scroll direction only if we
can't actually scroll in that direction, causing the white square where
neither scrollbar overlaps to appear at the lower right corner.

spec/editor-component-spec.coffee

@@ -547,6 +547,26 @@ describe "EditorComponent", ->
       bottomOfEditor = node.getBoundingClientRect().bottom
       expect(bottomOfLastLine).toBe bottomOfEditor
 
+    it "assigns the overflow to 'hidden' in the opposite direction unless the editor scrollable in that direction", ->
+      expect(verticalScrollbarNode.style.overflowX).toBe 'hidden'
+      expect(horizontalScrollbarNode.style.overflowY).toBe 'hidden'
+      return
+
+      node.style.height = 4.5 * lineHeightInPixels + 'px'
+      component.measureHeightAndWidth()
+      expect(verticalScrollbarNode.style.overflowX).toBe 'hidden'
+      expect(horizontalScrollbarNode.style.overflowY).toBe ''
+
+      node.style.width = 10 * charWidth + 'px'
+      component.measureHeightAndWidth()
+      expect(verticalScrollbarNode.style.overflowX).toBe ''
+      expect(horizontalScrollbarNode.style.overflowY).toBe ''
+
+      node.style.height = 20 * lineHeightInPixels + 'px'
+      component.measureHeightAndWidth()
+      expect(verticalScrollbarNode.style.overflowX).toBe ''
+      expect(horizontalScrollbarNode.style.overflowY).toBe 'hidden'
+
     describe "when a mousewheel event occurs on the editor", ->
       it "updates the horizontal or vertical scrollbar depending on which delta is greater (x or y)", ->
         node.style.height = 4.5 * lineHeightInPixels + 'px'