views::Textfield: Implement transpose editing command.

ui/views/controls/textfield/textfield_model.cc

Index: ui/views/controls/textfield/textfield_model.cc
diff --git a/ui/views/controls/textfield/textfield_model.cc b/ui/views/controls/textfield/textfield_model.cc
index d5bec8b33248d549600280d137186bbcf8557850..89e1caa12b396dedaae140124e8eefc15f404dc2 100644
--- a/ui/views/controls/textfield/textfield_model.cc
+++ b/ui/views/controls/textfield/textfield_model.cc
@@ -527,6 +527,36 @@ bool TextfieldModel::Paste() {
   return true;
 }
 
+bool TextfieldModel::Transpose() {
+  if (HasCompositionText() || HasSelection())
+    return false;
+
+  size_t cur = GetCursorPosition();
+  size_t next = render_text_->IndexOfAdjacentGrapheme(cur, gfx::CURSOR_FORWARD);
+  size_t prev =
+      render_text_->IndexOfAdjacentGrapheme(cur, gfx::CURSOR_BACKWARD);
+
+  // If we are at the end of the line, last two characters should be transposed.

[tapted, 2016/06/28 04:52:32]

nit: "If we are at .. line, last" -> "At .. line, the last"

[karandeepb, 2016/06/29 05:44:37]

Done.

+  if (cur == text().length()) {
+    DCHECK_EQ(cur, next);
+    cur = prev;
+    prev = render_text_->IndexOfAdjacentGrapheme(prev, gfx::CURSOR_BACKWARD);
+  }
+
+  // This happens when we are at the beginning of the line or the line has less

[tapted, 2016/06/28 04:52:32]

nit: remove "when we are", add `when` in "..line or when the line.."

[karandeepb, 2016/06/29 05:44:37]

Done.

+  // than two graphemes.
+  if (gfx::UTF16IndexToOffset(text(), prev, next) != 2)
+    return false;
+
+  SelectRange(gfx::Range(prev, next));
+  base::string16 text = GetSelectedText();
+  base::string16 transposed_text =
+      text.substr(cur - prev) + text.substr(0, cur - prev);

[tapted, 2016/06/28 04:52:32]

Should we add some emoji/surrogate pairs to
BridgedNativeWidgetTest::TestEditingCommands ?

[karandeepb, 2016/06/29 05:44:37]

Tried this but there are a few minor differences between how Views and
NSTextView handle emojis. For example for a string like 😊😎 NSTextView doesn't
transpose if we are at the end of the string. (probably an NSTextView bug). 
If at the string beginning and we do Alt+right (moveWordRight:),
Views::Textfield moves past both emojis while NSTextView moves past only the
first emoji.

[tapted, 2016/06/29 07:06:14]

Acknowledged.

+
+  InsertTextInternal(transposed_text, false);
+  return true;
+}

[tapted, 2016/06/28 04:52:32]

do you need to do anything special to get `undo` to work? Maybe that's another
good thing to include in BridgedNativeWidgetTest::TestEditingCommands -- i.e.
after PerformCommand, PerformCommand(@selector(undo:)) and see if they text and
selection matches.  (I suspect the selection currently will not..)

[karandeepb, 2016/06/29 05:44:37]

Undo behavior is not completely correct currently, not just for MacViews but
also on other platforms. I had filed a bug for this - http://crbug.com/615345
and plan to take it on later.

Regarding adding undo verification to
BridgedNativeWidgetTest::TestEditingCommands, it seems that action messages
performed using doCommandBySelector are not added to the undo stack for the
NSTextView. Will have to investigate how to get undo to work for these
programmatic NSTextView modifications, but that can probably wait till the undo
fix.

[tapted, 2016/06/29 07:06:14]

Acknowledged.

+
 bool TextfieldModel::HasSelection() const {
   return !render_text_->selection().is_empty();
 }