window.print() should close form validation bubble.

third_party/WebKit/Source/web/ValidationMessageClientImpl.h

Index: third_party/WebKit/Source/web/ValidationMessageClientImpl.h
diff --git a/third_party/WebKit/Source/web/ValidationMessageClientImpl.h b/third_party/WebKit/Source/web/ValidationMessageClientImpl.h
index 7ed0c7e42380ea511a5ba2682be5fa0c5a3f04db..1400d781bdfe2a8049874e9760c3d80c8b974e21 100644
--- a/third_party/WebKit/Source/web/ValidationMessageClientImpl.h
+++ b/third_party/WebKit/Source/web/ValidationMessageClientImpl.h
@@ -26,6 +26,7 @@
 #ifndef ValidationMessageClientImpl_h
 #define ValidationMessageClientImpl_h
 
+#include "core/page/PopupOpeningObserver.h"
 #include "core/page/ValidationMessageClient.h"
 #include "platform/Timer.h"
 #include "platform/geometry/IntRect.h"
@@ -39,7 +40,8 @@ class WebViewImpl;
 
 class ValidationMessageClientImpl final
     : public GarbageCollectedFinalized<ValidationMessageClientImpl>,
-      public ValidationMessageClient {
+      public ValidationMessageClient,
+      private PopupOpeningObserver {
   USING_GARBAGE_COLLECTED_MIXIN(ValidationMessageClientImpl);
 
  public:
@@ -64,6 +66,9 @@ class ValidationMessageClientImpl final
   void DocumentDetached(const Document&) override;
   void WillBeDestroyed() override;
 
+  // PopupOpeningObserver function
+  void WillOpenPopup() override;
+
   WebViewImpl& web_view_;
   Member<const Element> current_anchor_;
   String message_;