Stop propagation of keydown/textInput events to prevent React handler

React's global synthetic event handler is somewhat expensive. This
prevents it from being invoked on every keystroke, saving ~1ms.

src/editor-component.coffee

@@ -524,6 +524,12 @@ EditorComponent = React.createClass
     @refs.input.focus()
 
   onTextInput: (event) ->
+    event.stopPropagation()
+
+    # If we prevent the insertion of a space character, then the browser
+    # interprets the spacebar keypress as a page-down command.
+    event.preventDefault() unless event.data is ' '
+
     return unless @isInputEnabled()
 
     {editor} = @props
@@ -539,9 +545,6 @@ EditorComponent = React.createClass
     editor.insertText(event.data)
     inputNode.value = event.data
 
-    # If we prevent the insertion of a space character, then the browser
-    # interprets the spacebar keypress as a page-down command.
-    event.preventDefault() unless event.data is ' '
 
   onInputFocused: ->
     @setState(focused: true)

src/window-event-handler.coffee

@@ -57,8 +57,7 @@ class WindowEventHandler
 
     @subscribeToCommand $(document), 'core:focus-previous', @focusPrevious
 
-    @subscribe $(document), 'keydown', (event) ->
-      atom.keymaps.handleKeyboardEvent(event.originalEvent)
+    document.addEventListener 'keydown', @onKeydown
 
     @subscribe $(document), 'drop', (e) ->
       e.preventDefault()
@@ -95,6 +94,10 @@ class WindowEventHandler
     bindCommandToAction('core:redo', 'redo:')
     bindCommandToAction('core:select-all', 'selectAll:')
 
+  onKeydown: (event) ->
+    atom.keymaps.handleKeyboardEvent(event)
+    event.stopImmediatePropagation()
+
   openLink: ({target, currentTarget}) ->
     location = target?.getAttribute('href') or currentTarget?.getAttribute('href')
     if location and location[0] isnt '#' and /^https?:\/\//.test(location)