views: support vertical-drag-to-end on textfields

ui/views/style/platform_style.h

Index: ui/views/style/platform_style.h
diff --git a/ui/views/style/platform_style.h b/ui/views/style/platform_style.h
index e4240d49306a8920c8f6caf4f26d14b3a7459433..eb1a9086b34340e524488e16c553df13fbb44f16 100644
--- a/ui/views/style/platform_style.h
+++ b/ui/views/style/platform_style.h
@@ -20,6 +20,10 @@ class ScrollBar;
 // Cross-platform API for providing platform-specific styling for toolkit-views.
 class PlatformStyle {
  public:
+  // True if dragging vertically above or below a textfield's bounds selects to
+  // the beginning or end of the text from the cursor, respectively.
+  static const bool kTextfieldDragVerticallyDragsToEnd;
+
   // Creates the appropriate border for a focusable Combobox.
   static scoped_ptr<FocusableBorder> CreateComboboxBorder();