views::Textfield: Implement yank 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 7c6d5917f209fdcfbc0b5bb6c1c71ad1622e0044..45ab2aae843a85969761497602c6596e4e4ea5dc 100644
--- a/ui/views/controls/textfield/textfield_model.cc
+++ b/ui/views/controls/textfield/textfield_model.cc
@@ -8,6 +8,7 @@
 
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ -263,6 +264,24 @@ gfx::Range GetFirstEmphasizedRange(const ui::CompositionText& composition) {
   return gfx::Range::InvalidRange();
 }
 
+// Returns a reference to the kill buffer which holds the text to be inserted on
+// executing yank command. Singleton since it needs to be persisted across
+// multiple textfields.
+// On Mac, the size of the kill ring (no. of buffers) is controlled by
+// NSTextKillRingSize, a text system default. However to keep things simple,
+// the default kill ring size of 1 (i.e. a single buffer) is assumed.
+base::string16& GetKillBuffer() {

[sky, 2016/07/22 15:22:49]

return a pointer (references are generally restricted to const).

[karandeepb, 2016/07/25 06:38:11]

Done.

+  CR_DEFINE_STATIC_LOCAL(base::string16, kill_buffer, ());
+  DCHECK(base::MessageLoopForUI::IsCurrent());
+  return kill_buffer;
+}
+
+// Helper method to set the kill buffer.
+void SetKillBuffer(const base::string16& buffer) {
+  base::string16& kill_buffer = GetKillBuffer();
+  kill_buffer = buffer;
+}
+
 }  // namespace
 
 using internal::Edit;
@@ -325,13 +344,15 @@ void TextfieldModel::Append(const base::string16& new_text) {
   ClearSelection();
 }
 
-bool TextfieldModel::Delete() {
+bool TextfieldModel::Delete(bool add_to_kill_buffer) {
   if (HasCompositionText()) {
     // No undo/redo for composition text.
     CancelCompositionText();
     return true;
   }
   if (HasSelection()) {
+    if (add_to_kill_buffer)
+      SetKillBuffer(GetSelectedText());
     DeleteSelection();
     return true;
   }
@@ -339,20 +360,24 @@ bool TextfieldModel::Delete() {
     size_t cursor_position = GetCursorPosition();
     size_t next_grapheme_index = render_text_->IndexOfAdjacentGrapheme(
         cursor_position, gfx::CURSOR_FORWARD);
-    ExecuteAndRecordDelete(gfx::Range(cursor_position, next_grapheme_index),
-                           true);
+    gfx::Range range_to_delete(cursor_position, next_grapheme_index);
+    if (add_to_kill_buffer)
+      SetKillBuffer(GetTextFromRange(range_to_delete));
+    ExecuteAndRecordDelete(range_to_delete, true);
     return true;
   }
   return false;
 }
 
-bool TextfieldModel::Backspace() {
+bool TextfieldModel::Backspace(bool add_to_kill_buffer) {
   if (HasCompositionText()) {
     // No undo/redo for composition text.
     CancelCompositionText();
     return true;
   }
   if (HasSelection()) {
+    if (add_to_kill_buffer)
+      SetKillBuffer(GetSelectedText());
     DeleteSelection();
     return true;
   }
@@ -360,7 +385,10 @@ bool TextfieldModel::Backspace() {
   if (cursor_position > 0) {
     // Delete one code point, which may be two UTF-16 words.
     size_t previous_char = gfx::UTF16OffsetToIndex(text(), cursor_position, -1);

[msw, 2016/07/22 17:44:03]

optional nit: |previous_grapheme_index| for consistency with code above.

[karandeepb, 2016/07/25 06:38:11]

Done.

-    ExecuteAndRecordDelete(gfx::Range(cursor_position, previous_char), true);
+    gfx::Range range_to_delete(cursor_position, previous_char);
+    if (add_to_kill_buffer)
+      SetKillBuffer(GetTextFromRange(range_to_delete));
+    ExecuteAndRecordDelete(range_to_delete, true);
     return true;
   }
   return false;
@@ -557,6 +585,15 @@ bool TextfieldModel::Transpose() {
   return true;
 }
 
+bool TextfieldModel::Yank() {
+  const base::string16& kill_buffer = GetKillBuffer();
+  if (!kill_buffer.empty() || HasSelection()) {

[msw, 2016/07/22 17:44:03]

Why would this try to insert an empty string if there's a selection?

[karandeepb, 2016/07/25 06:38:11]

That's how Yank works on Mac/Cocoa. Open a new Chrome app instance, select some
text and press Ctrl+Y to yank. The selected text will get deleted (since kill
buffer is empty). 

[msw, 2016/07/25 18:35:49]

Ah, so it's just doing a delete in that case? Okay.

[karandeepb, 2016/07/26 03:45:41]

Yeah!

+    InsertTextInternal(kill_buffer, false);
+    return true;
+  }
+  return false;
+}
+
 bool TextfieldModel::HasSelection() const {
   return !render_text_->selection().is_empty();
 }
@@ -672,6 +709,11 @@ void TextfieldModel::ClearEditHistory() {
   current_edit_ = edit_history_.end();
 }
 
+// static
+void TextfieldModel::ClearKillBufferForTesting() {
+  SetKillBuffer(base::string16());
+}
+
 /////////////////////////////////////////////////////////////////
 // TextfieldModel: private