Add debug CHECK for WebView closing during input

Looking at code and the crash stacks, it looks like we're synchronously
closing a WebViewImpl while it's handling an input event.

This CL adds some debugging to crash earlier so we can get a stack
showing where the Close call is coming from.

Bug: 992315
Change-Id: I16b17cbbec6dfdafadfc334028a31227ae61ccae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769348
Commit-Queue: David Bokan <bokan@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691021}

third_party/blink/renderer/core/exported/web_view_impl.cc

@@ -1237,6 +1237,10 @@ void WebViewImpl::Close() {
     animation_host_ = nullptr;
   }
 
+  // TODO(bokan): Temporary debugging added to diagnose
+  // https://crbug.com/992315. Somehow we're synchronously calling
+  // WebViewImpl::Close while handling an input event.
+  CHECK(!debug_inside_input_handling_);
   AsView().page.Clear();
 
   // Reset the delegate to prevent notifications being sent as we're being
@@ -1690,6 +1694,12 @@ WebInputEventResult WebViewImpl::DispatchBufferedTouchEvents() {
 
 WebInputEventResult WebViewImpl::HandleInputEvent(
     const WebCoalescedInputEvent& coalesced_event) {
+  // TODO(bokan): Temporary debugging added to diagnose
+  // https://crbug.com/992315. Somehow we're synchronously calling
+  // WebViewImpl::Close while handling an input event.
+  base::AutoReset<bool> inside_input_handling(&debug_inside_input_handling_,
+                                              true);
+
   const WebInputEvent& input_event = coalesced_event.Event();
   // TODO(dcheng): The fact that this is getting called when there is no local
   // main frame is problematic and probably indicates a bug in the input event

third_party/blink/renderer/core/exported/web_view_impl.h

@@ -674,6 +674,11 @@ class CORE_EXPORT WebViewImpl final : public WebView,
   bool should_dispatch_first_layout_after_finished_loading_ = false;
   WebDisplayMode display_mode_ = kWebDisplayModeBrowser;
 
+  // TODO(bokan): Temporary debugging added to diagnose
+  // https://crbug.com/992315. Somehow we're synchronously calling
+  // WebViewImpl::Close while handling an input event.
+  bool debug_inside_input_handling_ = false;
+
   FloatSize elastic_overscroll_;
 
   Persistent<EventListener> popup_mouse_wheel_event_listener_;