Fix webview undefined exception

[AndrienkoAleksandr]

Referenced issue:

Part of the eclipse-che/che#13442

What it does

Fix webview undefined exception when webview located in the editor area(top area) and during restore editor tabs hide webview faster than it was rendered. Issue is reproducible on the Firefox.

How to test

1. Start theia with test theia plugin https://github.com/AndrienkoAleksandr/che-plugin-registry/releases/download/welcome-plugin-test/eclipse_che_welcome_plugin.theia
2. Open theia and open browser console by F12 (I used latest long term supported Firefox 68.0.1ers)

Exception log:

root ERROR ../../packages/plugin-ext/lib/main/browser/webview/webview.js/WebviewWidget.prototype.onBeforeHide@http://localhost:3000/43.bundle.js:2262:13
../../node_modules/@phosphor/widgets/lib/widget.js/Widget.prototype.processMessage@http://localhost:3000/bundle.js:26389:22
invokeHandler@http://localhost:3000/bundle.js:10313:21
sendMessage@http://localhost:3000/bundle.js:10049:13
../../node_modules/@phosphor/widgets/lib/widget.js/Widget.prototype.hide@http://localhost:3000/bundle.js:26301:37
../../node_modules/@phosphor/widgets/lib/dockpanel.js/DockPanel.prototype._onCurrentChanged@http://localhost:3000/bundle.js:16634:33
TheiaDockPanel/_this._onCurrentChanged@http://localhost:3000/bundle.js:125349:51
invokeSlot@http://localhost:3000/bundle.js:11098:18
emit@http://localhost:3000/bundle.js:11055:17
../../node_modules/@phosphor/signaling/lib/index.js/</Signal.prototype.emit@http://localhost:3000/bundle.js:10728:17
set@http://localhost:3000/bundle.js:24207:34
set@http://localhost:3000/bundle.js:24165:54
../../node_modules/@phosphor/widgets/lib/dockpanel.js/DockPanel.prototype.selectWidget@http://localhost:3000/bundle.js:16091:9
../../node_modules/@phosphor/widgets/lib/dockpanel.js/DockPanel.prototype.activateWidget@http://localhost:3000/bundle.js:16102:14
../../packages/core/lib/browser/shell/theia-dock-panel.js/TheiaDockPanel.prototype.activateWidget@http://localhost:3000/bundle.js:125394:41
../../packages/core/lib/browser/shell/application-shell.js/ApplicationShell.prototype.doActivateWidget@http://localhost:3000/bundle.js:121718:28
../../packages/core/lib/browser/shell/application-shell.js/ApplicationShell.prototype.activateWidget@http://localhost:3000/bundle.js:121697:30
../../packages/core/lib/browser/widget-open-handler.js/WidgetOpenHandler.prototype.doOpen/</<@http://localhost:3000/bundle.js:133037:40
step@http://localhost:3000/bundle.js:132976:23
verb/<@http://localhost:3000/bundle.js:132957:53
../../packages/core/lib/browser/widget-open-handler.js/__awaiter</<@http://localhost:3000/bundle.js:132951:71
../../packages/core/lib/browser/widget-open-handler.js/__awaiter<@http://localhost:3000/bundle.js:132947:12
../../packages/core/lib/browser/widget-open-handler.js/WidgetOpenHandler.prototype.doOpen@http://localhost:3000/bundle.js:133024:16
../../packages/core/lib/browser/widget-open-handler.js/WidgetOpenHandler.prototype.open/</<@http://localhost:3000/bundle.js:133015:51
step@http://localhost:3000/bundle.js:132976:23
verb/<@http://localhost:3000/bundle.js:132957:53
fulfilled@http://localhost:3000/bundle.js:132948:58

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

Signed-off-by: Oleksandr Andriienko oandriie@redhat.com

[akosyakov]

We are targeting to land the proper support of webviews #6465 please help to test and review it instead

[benoitf]

@akosyakov is reworking webviews as part of #6465

So need to check if it's working in his PR

[akosyakov]

FireFox support is generally broken right now: #6582 If you rebase the PR it won't start the app. One can test by excluding the plugin-metrics from the build though.

[akosyakov]

#6582 landed instead