Correct validation popup hiding code

When the validation popup is hidden, this unexpected code path occurs:
- HideValidationMessage() is called continuously, and keeps restarting
the timer used to call Reset()
- As a result, Reset() is never reached

The fix: do not restart the timer if a hide is in progress.

This fix is blocking an accessibility fix, which needs an accurate signal
when the validation message is no longer visible.

Bug: None
Change-Id: I0d69abf006a881dd7cc147dfe49ada50217b8c4a
Reviewed-on: https://chromium-review.googlesource.com/c/1417890Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625241}

third_party/blink/renderer/core/page/validation_message_client_impl.cc

@@ -99,8 +99,12 @@ void ValidationMessageClientImpl::HideValidationMessage(const Element& anchor) {
     HideValidationMessageImmediately(anchor);
     return;
   }
-  if (!current_anchor_ || !IsValidationMessageVisible(anchor))
+  if (!current_anchor_ || !IsValidationMessageVisible(anchor) ||
+      overlay_delegate_->IsHiding()) {
+    // Do not continue if already hiding, otherwise timer will never complete
+    // and Reset() is never called.
     return;
+  }
   DCHECK(overlay_);
   overlay_delegate_->StartToHide();
   timer_ = std::make_unique<TaskRunnerTimer<ValidationMessageClientImpl>>(

third_party/blink/renderer/core/page/validation_message_overlay_delegate.h

@@ -38,6 +38,7 @@ class ValidationMessageOverlayDelegate : public FrameOverlay::Delegate {
                          GraphicsContext&,
                          const IntSize& view_size) const override;
   void StartToHide();
+  bool IsHiding() const;
 
  private:
   ValidationMessageOverlayDelegate(Page&,
@@ -52,7 +53,6 @@ class ValidationMessageOverlayDelegate : public FrameOverlay::Delegate {
   void WriteDocument(SharedBuffer*);
   Element& GetElementById(const AtomicString&) const;
   void AdjustBubblePosition(const IntSize& view_size);
-  bool IsHiding() const;
 
   // An internal Page and a ChromeClient for it.
   Persistent<Page> page_;