Relativize pixelPositionForScreenPosition.top

This commit makes the method return a `top` value which is relative to the
viewport. However, we still need to return an absolute value for `left` because
lines are moved horizontally through a single transform on their parent node.

I would prefer being consistent (i.e. make everything relative), but moving
every single tile to simulate scrolling, on the other hand, seems overkill and
it's not really intuitive given that we are not tiling horizontally.

/cc: @nathansobo

src/text-editor-presenter.coffee

@@ -375,11 +375,11 @@ class TextEditorPresenter
       else
         screenPosition = decoration.getMarker().getHeadScreenPosition()
 
-      pixelPosition = @pixelPositionForScreenPosition(screenPosition, true, absolute: true)
+      pixelPosition = @pixelPositionForScreenPosition(screenPosition, true)
 
-      {scrollTop, scrollLeft} = @state.content
+      {scrollLeft} = @state.content
 
-      top = pixelPosition.top + @lineHeight - scrollTop
+      top = pixelPosition.top + @lineHeight
       left = pixelPosition.left + @gutterWidth - scrollLeft
 
       if overlayDimensions = @overlayDimensions[decoration.id]
@@ -963,7 +963,7 @@ class TextEditorPresenter
   hasPixelPositionRequirements: ->
     @lineHeight? and @baseCharacterWidth?
 
-  pixelPositionForScreenPosition: (screenPosition, clip=true, {absolute}={}) ->
+  pixelPositionForScreenPosition: (screenPosition, clip=true) ->
     screenPosition = Point.fromObject(screenPosition)
     screenPosition = @model.clipScreenPosition(screenPosition) if clip
 
@@ -993,7 +993,7 @@ class TextEditorPresenter
         left += characterWidths[char] ? baseCharacterWidth unless char is '\0'
         column += charLength
 
-    top -= @scrollTop unless absolute
+    top -= @scrollTop
     {top, left}
 
   hasPixelRectRequirements: ->