Make DeleteSelectionCommand to handle ::first-letter correctly

This patch changes |DeleteSelectionCommand::HandleGeneralDelete()| to use the
clean layout tree for calling |start_node->GetLayoutObject()| after calling
|DeleteTextFromNode()| or |RemoveChildrenInRange()| to avoid removing
|start_node|.


Note: When |Text| node with ::first-letter is modified, Blink detach
layout object from it in |Text::UpdateTextLayoutObject()| to follow
|ShouldUpdateLayoutByReattaching()| which returns true for |true| for
|Text| node with ::first-letter.

Bug: 808516
Change-Id: I7139398ca3938e56960c81c9196bd58e91bed668
Reviewed-on: https://chromium-review.googlesource.com/920051
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537233}

third_party/WebKit/Source/core/editing/commands/DeleteSelectionCommand.cpp

@@ -677,6 +677,8 @@ void DeleteSelectionCommand::HandleGeneralDelete(EditingState* editing_state) {
           return;
         ending_position_ = upstream_start_;
       }
+      // We should update layout to associate |start_node| to layout object.
+      GetDocument().UpdateStyleAndLayoutIgnorePendingStylesheets();
     }
 
     // The selection to delete is all in one node.

third_party/WebKit/Source/core/editing/commands/DeleteSelectionCommandTest.cpp

@@ -62,4 +62,21 @@ TEST_F(DeleteSelectionCommandTest, deleteListFromTable) {
                                   .ToOffsetInAnchor());
 }
 
+TEST_F(DeleteSelectionCommandTest, ForwardDeleteWithFirstLetter) {
+  InsertStyleElement("p::first-letter {font-size:200%;}");
+  Selection().SetSelectionAndEndTyping(
+      SetSelectionTextToBody("<p contenteditable>a^b|c</p>"));
+
+  const bool kNoSmartDelete = false;
+  const bool kMergeBlocksAfterDelete = true;
+  const bool kNoExpandForSpecialElements = false;
+  const bool kSanitizeMarkup = true;
+  DeleteSelectionCommand& command = *DeleteSelectionCommand::Create(
+      GetDocument(), kNoSmartDelete, kMergeBlocksAfterDelete,
+      kNoExpandForSpecialElements, kSanitizeMarkup);
+  EXPECT_TRUE(command.Apply()) << "the delete command should have succeeded";
+  EXPECT_EQ("<p contenteditable>a|c</p>",
+            GetSelectionTextFromBody(Selection().GetSelectionInDOMTree()));
+}
+
 }  // namespace blink