Make Editor::CanCopy() to use flat tree version of selection

This patch changes |Editor::CanCopy()| to use flat tree version of selection
instead of DOM tree version since serialization for "copy" command traverses
flat tree, to allow users to copy selection crossing shadow boundary.

Bug: 866175
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I89152cf2843a39af6197ef3aa9153f72fd728ad9
Reviewed-on: https://chromium-review.googlesource.com/1149940
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578216}

third_party/blink/renderer/core/editing/editor.cc

@@ -238,9 +238,12 @@ bool Editor::CanCopy() const {
   FrameSelection& selection = GetFrameSelection();
   if (!selection.IsAvailable())
     return false;
-  return selection.ComputeVisibleSelectionInDOMTreeDeprecated().IsRange() &&
+  frame_->GetDocument()->UpdateStyleAndLayoutIgnorePendingStylesheets();
+  const VisibleSelectionInFlatTree& visible_selection =
+      selection.ComputeVisibleSelectionInFlatTree();
+  return visible_selection.IsRange() &&
          !IsInPasswordFieldWithUnrevealedPassword(
-             selection.ComputeVisibleSelectionInDOMTree().Start());
+             ToPositionInDOMTree(visible_selection.Start()));
 }
 
 bool Editor::CanPaste() const {

third_party/blink/renderer/core/editing/editor_test.cc

@@ -6,6 +6,8 @@
 
 #include "third_party/blink/renderer/core/clipboard/system_clipboard.h"
 #include "third_party/blink/renderer/core/editing/commands/editor_command.h"
+#include "third_party/blink/renderer/core/editing/frame_selection.h"
+#include "third_party/blink/renderer/core/editing/selection_template.h"
 #include "third_party/blink/renderer/core/editing/testing/editing_test_base.h"
 #include "third_party/blink/renderer/core/html/forms/html_input_element.h"
 #include "third_party/blink/renderer/platform/testing/unit_test_helpers.h"
@@ -26,6 +28,13 @@ class EditorTest : public EditingTestBase {
   }
 };
 
+TEST_F(EditorTest, CanCopyCrossingShadowBoundary) {
+  const SelectionInDOMTree selection = SetSelectionTextToBody(
+      "<p><template data-mode=open>^abc</template></p><b>|</b>");
+  Selection().SetSelection(selection, SetSelectionOptions());
+  EXPECT_TRUE(GetDocument().GetFrame()->GetEditor().CanCopy());
+}
+
 TEST_F(EditorTest, copyGeneratedPassword) {
   // Checks that if the password field has the value generated by Chrome
   // (HTMLInputElement::shouldRevealPassword will be true), copying the field