[WebView Autofill] Post DidChangeScrollOffset outside PerformLayout

If LocalFrameView::PerformLayout() ends up calling
LocalFrameView::ViewportSizeChanged(), then
it may in turn call AutofillAgent::DidChangeScrollOffset().

However, FindFormAndFieldForFormControlElement() and
ElementBoundsInWindow() requires that document life cycle to be
mutatable (and thus not in the middle of perform layout).

Therefore, posting a task to delay calling these functions outside
PerformLayout().

Note that this uses a similar mechanism as
FormTracker::TextFieldDidChange().

BUG=804886

Change-Id: Ibe6e6d9921185f075d16c6c955d45d17ad490fd5
Reviewed-on: https://chromium-review.googlesource.com/882664
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Commit-Queue: Changwan Ryu <changwan@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#531528}(cherry picked from commit 9db32db)
Reviewed-on: https://chromium-review.googlesource.com/884265
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#68}
Cr-Branched-From: bc084a8-refs/heads/master@{#530369}

Author: Changwan Ryu

components/autofill/content/renderer/autofill_agent.cc

@@ -212,22 +212,36 @@ void AutofillAgent::DidFinishDocumentLoad() {
 }
 
 void AutofillAgent::DidChangeScrollOffset() {
-  if (!focus_requires_scroll_ && is_popup_possibly_visible_ &&
-      element_.Focused()) {
-    FormData form;
-    FormFieldData field;
-    if (form_util::FindFormAndFieldForFormControlElement(element_, &form,
-                                                         &field)) {
-      GetAutofillDriver()->TextFieldDidScroll(
-          form, field,
-          render_frame()->GetRenderView()->ElementBoundsInWindow(element_));
-    }
+  if (!focus_requires_scroll_) {
+    // Post a task here since scroll offset may change during layout.
+    // (https://crbug.com/804886)
+    weak_ptr_factory_.InvalidateWeakPtrs();
+    base::SequencedTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::BindOnce(&AutofillAgent::DidChangeScrollOffsetImpl,
+                                  weak_ptr_factory_.GetWeakPtr(), element_));
+  } else if (!IsKeyboardAccessoryEnabled()) {
+    HidePopup();
   }
+}
 
-  if (IsKeyboardAccessoryEnabled())
+void AutofillAgent::DidChangeScrollOffsetImpl(
+    const WebFormControlElement& element) {
+  if (element != element_ || focus_requires_scroll_ ||
+      !is_popup_possibly_visible_ || !element_.Focused())
     return;
 
-  HidePopup();
+  FormData form;
+  FormFieldData field;
+  if (form_util::FindFormAndFieldForFormControlElement(element_, &form,
+                                                       &field)) {
+    GetAutofillDriver()->TextFieldDidScroll(
+        form, field,
+        render_frame()->GetRenderView()->ElementBoundsInWindow(element_));
+  }
+
+  // Ignore subsequent scroll offset changes.
+  if (!IsKeyboardAccessoryEnabled())
+    HidePopup();
 }
 
 void AutofillAgent::FocusedNodeChanged(const WebNode& node) {

components/autofill/content/renderer/autofill_agent.h

@@ -193,6 +193,7 @@ class AutofillAgent : public content::RenderFrameObserver,
   FRIEND_TEST_ALL_PREFIXES(FormAutocompleteTest, CollectFormlessElements);
 
   void OnTextFieldDidChange(const blink::WebInputElement& element);
+  void DidChangeScrollOffsetImpl(const blink::WebFormControlElement& element);
 
   // Shows the autofill suggestions for |element|. This call is asynchronous
   // and may or may not lead to the showing of a suggestion popup (no popup is