Insert a line break when space is inserted at the top of wrapped lines

third_party/WebKit/Source/core/editing/Editor.cpp

Index: third_party/WebKit/Source/core/editing/Editor.cpp
diff --git a/third_party/WebKit/Source/core/editing/Editor.cpp b/third_party/WebKit/Source/core/editing/Editor.cpp
index 79d38cb36fe377f0d516a531a5b4fb95d4f2a6f6..1d6608c3f66698dc41aac0aa7e343a6e9ed1e501 100644
--- a/third_party/WebKit/Source/core/editing/Editor.cpp
+++ b/third_party/WebKit/Source/core/editing/Editor.cpp
@@ -201,6 +201,18 @@ EditorClient& Editor::client() const {
   return emptyEditorClient();
 }
 
+static bool isCaretAtTopOfWrappedLine(FrameSelection& selection) {
+  if (!selection.isCaret())
+    return false;
+  if (selection.affinity() != TextAffinity::Downstream)
+    return false;
+  // Enable this operation for plaintext only for now.
+  if (selection.isContentRichlyEditable())
+    return false;
+  // TODO(kojii): how to know if a Position is at the top of wrapped line?

[yosin_UTC9, 2017/01/05 08:36:50]

I think "start" is better than "top".

We can check this by

const Position& position = selection.start();

bool isStartOfWrappedLine = !InSameLine(
  PositionWithAffinity(position, TextAffinity::Upstream), 
  PositionWithAffinity(position, TextAffinity::Downstream));

If |position| is at start of wrapped line, VP(pos, Up) and VP(pos, Down) are in
different line.
VisiblePosition:create() does similar check to return VP(pos, Down) if VP(pos,
Down) and VP(pos, Up) are in same line.

+  return true;
+}
+
 bool Editor::handleTextEvent(TextEvent* event) {
   // Default event handling for Drag and Drop will be handled by DragController
   // so we leave the event for it.
@@ -237,6 +249,9 @@ bool Editor::handleTextEvent(TextEvent* event) {
     return insertParagraphSeparator();
   }
 
+  if (data == " " && isCaretAtTopOfWrappedLine(frame().selection()))
+    insertLineBreak();
+
   return insertTextWithoutSendingTextEvent(EditCommandSource::kMenuOrKeyBinding,
                                            data, false, event);
 }