Don't set contentWindow property for <webview>

This property is only available in Chrome and we don't need it in
atom-shell, so remove it to avoid confusions.

Fixes #997.

atom/browser/lib/guest-view-manager.coffee

@@ -115,9 +115,8 @@ destroyGuest = (id) ->
 ipc.on 'ATOM_SHELL_GUEST_VIEW_MANAGER_CREATE_GUEST', (event, type, params, requestId) ->
   event.sender.send "ATOM_SHELL_RESPONSE_#{requestId}", createGuest(event.sender, params)
 
-ipc.on 'ATOM_SHELL_GUEST_VIEW_MANAGER_ATTACH_GUEST', (event, elementInstanceId, guestInstanceId, params, requestId) ->
+ipc.on 'ATOM_SHELL_GUEST_VIEW_MANAGER_ATTACH_GUEST', (event, elementInstanceId, guestInstanceId, params) ->
   attachGuest event.sender, elementInstanceId, guestInstanceId, params
-  event.sender.send "ATOM_SHELL_RESPONSE_#{requestId}"
 
 ipc.on 'ATOM_SHELL_GUEST_VIEW_MANAGER_DESTROY_GUEST', (event, id) ->
   destroyGuest id

atom/renderer/lib/web-view/guest-view-internal.coffee

@@ -45,10 +45,8 @@ module.exports =
     ipc.send 'ATOM_SHELL_GUEST_VIEW_MANAGER_CREATE_GUEST', type, params, requestId
     ipc.once "ATOM_SHELL_RESPONSE_#{requestId}", callback
 
-  attachGuest: (elementInstanceId, guestInstanceId, params, callback) ->
-    requestId++
-    ipc.send 'ATOM_SHELL_GUEST_VIEW_MANAGER_ATTACH_GUEST', elementInstanceId, guestInstanceId, params, requestId
-    ipc.once "ATOM_SHELL_RESPONSE_#{requestId}", callback
+  attachGuest: (elementInstanceId, guestInstanceId, params) ->
+    ipc.send 'ATOM_SHELL_GUEST_VIEW_MANAGER_ATTACH_GUEST', elementInstanceId, guestInstanceId, params
     webFrame.attachGuest elementInstanceId
 
   destroyGuest: (guestInstanceId) ->

atom/renderer/lib/web-view/web-view-constants.coffee

@@ -22,8 +22,5 @@ module.exports =
   ERROR_MSG_ALREADY_NAVIGATED: 'The object has already navigated, so its partition cannot be changed.'
   ERROR_MSG_CANNOT_INJECT_SCRIPT: '<webview>: ' +
       'Script cannot be injected into content until the page has loaded.'
-  ERROR_MSG_CONTENTWINDOW_NOT_AVAILABLE: '<webview>: ' +
-      'contentWindow is not available at this time. It will become available ' +
-      'when the page has finished loading.'
   ERROR_MSG_INVALID_PARTITION_ATTRIBUTE: 'Invalid partition attribute.'
   ERROR_MSG_INVALID_PRELOAD_ATTRIBUTE: 'Only "file:" or "asar:" protocol is supported in "preload" attribute.'

atom/renderer/lib/web-view/web-view.coffee

@@ -17,7 +17,6 @@ class WebViewImpl
     @elementAttached = false
 
     @beforeFirstNavigation = true
-    @contentWindow = null
 
     # on* Event handlers.
     @on = {}
@@ -26,7 +25,6 @@ class WebViewImpl
     shadowRoot = @webviewNode.createShadowRoot()
     @setupWebViewAttributes()
     @setupFocusPropagation()
-    @setupWebviewNodeProperties()
 
     @viewInstanceId = getNextId()
 
@@ -54,7 +52,6 @@ class WebViewImpl
       @guestInstanceId = undefined
       @beforeFirstNavigation = true
       @attributes[webViewConstants.ATTRIBUTE_PARTITION].validPartitionId = true
-      @contentWindow = null
     @internalInstanceId = 0
 
   # Sets the <webview>.request property.
@@ -75,16 +72,6 @@ class WebViewImpl
       # Blur the BrowserPlugin when the <webview> loses focus.
       @browserPluginNode.blur()
 
-  setupWebviewNodeProperties: ->
-    # We cannot use {writable: true} property descriptor because we want a
-    # dynamic getter value.
-    Object.defineProperty @webviewNode, 'contentWindow',
-      get: =>
-        return @contentWindow if @contentWindow?
-        window.console.error webViewConstants.ERROR_MSG_CONTENTWINDOW_NOT_AVAILABLE
-      # No setter.
-      enumerable: true
-
   # This observer monitors mutations to attributes of the <webview> and
   # updates the BrowserPlugin properties accordingly. In turn, updating
   # a BrowserPlugin property will update the corresponding BrowserPlugin
@@ -104,7 +91,7 @@ class WebViewImpl
 
       return unless @guestInstanceId
 
-      guestViewInternal.attachGuest @internalInstanceId, @guestInstanceId, @buildAttachParams(), (w) => @contentWindow = w
+      guestViewInternal.attachGuest @internalInstanceId, @guestInstanceId, @buildAttachParams()
 
   onSizeChanged: (webViewEvent) ->
     newWidth = webViewEvent.newWidth
@@ -189,7 +176,7 @@ class WebViewImpl
 
     return true unless @internalInstanceId
 
-    guestViewInternal.attachGuest @internalInstanceId, @guestInstanceId, params, (w) => @contentWindow = w
+    guestViewInternal.attachGuest @internalInstanceId, @guestInstanceId, params
 
 # Registers browser plugin <object> custom element.
 registerBrowserPluginElement = ->