Purge web view on renderer crash.

On iOS 11 WKWebView does not repaint after crash and reload. Recreating
web view fixes the issue.

It seems like the problem is not reproducible if web view scroll view
remain in the default position, but it's impossible to check if web view
was scrolled once the renderer has crashed. Recreating web view should
not have visible performance implications, so it will be more reliable to
purge it unconditionally if renderer has crashed.

Bug: 770914
Change-Id: I84feede9e54e4371aaf36b47db0fc9878e7518a9
Reviewed-on: https://chromium-review.googlesource.com/727401
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510101}

ios/web/web_state/ui/crw_web_controller.mm

@@ -3958,6 +3958,12 @@ registerLoadRequestForURL:(const GURL&)requestURL
   _webProcessCrashed = YES;
   _webStateImpl->CancelDialogs();
   _webStateImpl->OnRenderProcessGone();
+  if (@available(iOS 11, *)) {
+    // On iOS 11 WKWebView does not repaint after crash and reload. Recreating
+    // web view fixes the issue. TODO(crbug.com/770914): Remove this workaround
+    // once rdar://35063950 is fixed.
+    [self removeWebView];
+  }
 }
 
 - (web::WKWebViewConfigurationProvider&)webViewConfigurationProvider {