Store useShadowDOM setting when TextEditorElement is created

Rather than reading it repeatedly, since the value could potentially
change over time.

src/lines-component.coffee

@@ -59,7 +59,7 @@ LinesComponent = React.createClass
     @renderedDecorationsByLineId = {}
 
   componentDidMount: ->
-    if atom.config.get('editor.useShadowDOM')
+    if @props.useShadowDOM
       insertionPoint = document.createElement('content')
       insertionPoint.setAttribute('select', '.overlayer')
       @getDOMNode().appendChild(insertionPoint)

src/text-editor-component.coffee

@@ -50,7 +50,7 @@ TextEditorComponent = React.createClass
 
   render: ->
     {focused, showIndentGuide, showLineNumbers, visible} = @state
-    {editor, mini, cursorBlinkPeriod, cursorBlinkResumeDelay, hostElement} = @props
+    {editor, mini, cursorBlinkPeriod, cursorBlinkResumeDelay, hostElement, useShadowDOM} = @props
     maxLineNumberDigits = editor.getLineCount().toString().length
     hasSelection = editor.getLastSelection()? and !editor.getLastSelection().isEmpty()
     style = {}
@@ -117,7 +117,7 @@ TextEditorComponent = React.createClass
           @scrollingVertically, scrollHeight, scrollWidth, mouseWheelScreenRow,
           visible, scrollViewHeight, @scopedCharacterWidthsChangeCount, lineWidth, @useHardwareAcceleration,
           placeholderText, @performedInitialMeasurement, @backgroundColor, cursorPixelRects,
-          cursorBlinkPeriod, cursorBlinkResumeDelay, mini
+          cursorBlinkPeriod, cursorBlinkResumeDelay, mini, useShadowDOM
         }
 
         ScrollbarComponent

src/text-editor-element.coffee

@@ -28,6 +28,8 @@ class TextEditorElement extends HTMLElement
     @setAttribute('tabindex', -1)
 
     if atom.config.get('editor.useShadowDOM')
+      @useShadowDOM = true
+
       unless ShadowStyleSheet?
         ShadowStyleSheet = document.createElement('style')
         ShadowStyleSheet.textContent = atom.themes.loadLessStylesheet(require.resolve('../static/text-editor-shadow.less'))
@@ -45,6 +47,8 @@ class TextEditorElement extends HTMLElement
       @shadowRoot.appendChild(@stylesElement)
       @shadowRoot.appendChild(@rootElement)
     else
+      @useShadowDOM = false
+
       @stylesElement = document.head.querySelector('atom-styles')
       @rootElement = this
 
@@ -95,10 +99,11 @@ class TextEditorElement extends HTMLElement
       editor: @model
       mini: @model.mini
       lineOverdrawMargin: @lineOverdrawMargin
+      useShadowDOM: @useShadowDOM
     )
     @component = React.renderComponent(@componentDescriptor, @rootElement)
 
-    unless atom.config.get('editor.useShadowDOM')
+    unless @useShadowDOM
       inputNode = @component.refs.input.getDOMNode()
       inputNode.addEventListener 'focus', @focused.bind(this)
       inputNode.addEventListener 'blur', => @dispatchEvent(new FocusEvent('blur', bubbles: false))
@@ -116,7 +121,7 @@ class TextEditorElement extends HTMLElement
       @focusOnAttach = true
 
   blurred: (event) ->
-    unless atom.config.get('editor.useShadowDOM')
+    unless @useShadowDOM
       if event.relatedTarget is @component?.refs.input?.getDOMNode()
         event.stopImmediatePropagation()
         return