Blur immediately if an attribute change made an element unfocasable.

third_party/WebKit/Source/core/html/HTMLElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLElement.cpp b/third_party/WebKit/Source/core/html/HTMLElement.cpp
index 30bc4d81d68450103a6e24390c9557188f344936..d48fe0f5d50283720ec93018fdbabbc626cded88 100644
--- a/third_party/WebKit/Source/core/html/HTMLElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLElement.cpp
@@ -426,6 +426,26 @@ const AtomicString& HTMLElement::eventNameForAttributeName(
   return attributeNameToEventNameMap.get(attrName.localName());
 }
 
+void HTMLElement::attributeChanged(const QualifiedName& name,
+                                   const AtomicString& oldValue,
+                                   const AtomicString& newValue,
+                                   AttributeModificationReason reason) {
+  Element::attributeChanged(name, oldValue, newValue, reason);
+  if (reason != AttributeModificationReason::kDirectly)
+    return;
+  if (adjustedFocusedElementInTreeScope() != this)
+    return;
+  if (name == hiddenAttr && !newValue.isNull()) {
+    blur();
+  } else if (name == contenteditableAttr) {
+    // supportsFocus() behavior depends on element classes. It's hard to avoid
+    // to call it, and it needs up-to-date style.
+    document().updateStyleAndLayoutTreeForNode(this);
+    if (!supportsFocus())
+      blur();
+  }
+}
+
 void HTMLElement::parseAttribute(const QualifiedName& name,
                                  const AtomicString& oldValue,
                                  const AtomicString& value) {