MacViews: Correct behavior of move and select commands when selection direction changes.

ui/gfx/text_constants.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_TEXT_CONSTANTS_H_
 #define UI_GFX_TEXT_CONSTANTS_H_
 
 namespace gfx {
 
 // TODO(msw): Distinguish between logical character stops and glyph stops?
 // TODO(msw): Merge with base::i18n::BreakIterator::BreakType.
 enum BreakType {
   CHARACTER_BREAK = 0, // Stop cursor movement on neighboring characters.
   WORD_BREAK,          // Stop cursor movement on nearest word boundaries.
   LINE_BREAK,          // Stop cursor movement on line ends as shown on screen.
 };
 
+// Specifies how a move and select command behaves if the selection direction
+// is reversed. For example consider the state "ab|cd|e", i.e. cd is selected.
+// Assume the selection direction is from left to right. If we move to the
+// beginning of the line while modifying the selection, the resultant state is:
+// "|ab|cde" for SELECTION_START_NEW, selection direction from right to left.
+// "|abcd|e" for SELECTION_EXTEND, selection direction from right to left.
+// "ab|cde" for SELECTION_CARET.
+enum SelectionReversedBehavior {
+  // Existing selection is deselcted and a new selection is started in the
+  // opposite direction. Default.
+  SELECTION_START_NEW,
+
+  // The existing selection is extended in the opposite direction.

[tapted, 2016/05/20 06:47:36]

Might be good to give an example of a particular case this is for. E.g. "This is
the behavior for textfields on Mac when doing <blah>". Same for SELECTION_CARET

[karandeepb, 2016/05/24 07:47:15]

Done.

+  SELECTION_EXTEND,
+
+  // The existing selection reduces to a caret.
+  SELECTION_CARET,
+
+  SELECTION_DEFAULT = SELECTION_START_NEW,
+};
+
 // Specifies the word wrapping behavior when a word would exceed the available
 // display width. All words that are too wide will be put on a new line, and
 // then:
 enum WordWrapBehavior {
   IGNORE_LONG_WORDS,   // Overflowing word text is left on that line.
   TRUNCATE_LONG_WORDS, // Overflowing word text is truncated.
   ELIDE_LONG_WORDS,    // Overflowing word text is elided at the ellipsis.
   WRAP_LONG_WORDS,     // Overflowing word text is wrapped over multiple lines.
 };
 
@@ skipping 50 matching lines @@
   ELIDE_HEAD,   // Add an ellipsis at the start of the string.
   ELIDE_MIDDLE, // Add an ellipsis in the middle of the string.
   ELIDE_TAIL,   // Add an ellipsis at the end of the string.
   ELIDE_EMAIL,  // Add ellipses to username and domain substrings.
   FADE_TAIL,    // Fade the string's end opposite of its horizontal alignment.
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_TEXT_CONSTANTS_H_