Remove opaque backgrounds on mini editors

Fixes #3239

spec/editor-component-spec.coffee

@@ -2103,6 +2103,9 @@ describe "EditorComponent", ->
     it "adds the 'mini' class to the wrapper view", ->
       expect(wrapperNode.classList.contains('mini')).toBe true
 
+    it "does not have an opaque background on lines", ->
+      expect(component.refs.lines.getDOMNode().getAttribute('style')).not.toContain 'background-color'
+
     it "does not render invisible characters", ->
       component.setInvisibles(eol: 'E')
       component.setShowInvisibles(true)

src/editor-component.coffee

@@ -112,7 +112,7 @@ EditorComponent = React.createClass
           @scrollingVertically, scrollHeight, scrollWidth, mouseWheelScreenRow, invisibles,
           @visible, scrollViewHeight, @scopedCharacterWidthsChangeCount, lineWidth, @useHardwareAcceleration,
           placeholderText, @performedInitialMeasurement, @backgroundColor, cursorPixelRects,
-          cursorBlinkPeriod, cursorBlinkResumeDelay
+          cursorBlinkPeriod, cursorBlinkResumeDelay, mini
         }
 
         ScrollbarComponent

src/lines-component.coffee

@@ -22,12 +22,12 @@ LinesComponent = React.createClass
     if performedInitialMeasurement
       {editor, highlightDecorations, scrollHeight, scrollWidth, placeholderText, backgroundColor} = @props
       {lineHeightInPixels, defaultCharWidth, scrollViewHeight, scopedCharacterWidthsChangeCount} = @props
-      {scrollTop, scrollLeft, cursorPixelRects} = @props
+      {scrollTop, scrollLeft, cursorPixelRects, mini} = @props
       style =
         height: Math.max(scrollHeight, scrollViewHeight)
         width: scrollWidth
         WebkitTransform: @getTransform()
-        backgroundColor: backgroundColor
+        backgroundColor: if mini then null else backgroundColor
 
     div {className: 'lines', style},
       div className: 'placeholder-text', placeholderText if placeholderText?