views: support Mac textfield-focus behavior

On Mac, textfields always scroll to the start when gaining or losing focus;
this change implements that by:

1) On keyboard focus, doing a reversed SelectAll, so that the new selection
   "ends" at the logical start on Mac;
2) In OnBlur(), moving the selection to the logical start if PlatformStyle
   calls for same

Bug: 657558
Change-Id: I81c01f6ae5a546f1abb51a28638091907379d04e
Reviewed-on: https://chromium-review.googlesource.com/598122Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491723}

ui/views/controls/textfield/textfield.cc

@@ -803,7 +803,7 @@ bool Textfield::CanHandleAccelerators() const {
 }
 
 void Textfield::AboutToRequestFocusFromTabTraversal(bool reverse) {
-  SelectAll(false);
+  SelectAll(PlatformStyle::kTextfieldScrollsToStartOnFocusChange);
 }
 
 bool Textfield::SkipDefaultKeyEventProcessing(const ui::KeyEvent& event) {
@@ -1036,6 +1036,11 @@ void Textfield::OnFocus() {
 void Textfield::OnBlur() {
   gfx::RenderText* render_text = GetRenderText();
   render_text->set_focused(false);
+
+  // If necessary, yank the cursor to the logical start of the textfield.
+  if (PlatformStyle::kTextfieldScrollsToStartOnFocusChange)
+    model_->MoveCursorTo(gfx::SelectionModel(0, gfx::CURSOR_FORWARD));
+
   if (GetInputMethod()) {
     GetInputMethod()->DetachTextInputClient(this);
 #if defined(OS_CHROMEOS)

ui/views/style/platform_style.cc

@@ -50,6 +50,7 @@ const bool PlatformStyle::kTreeViewSelectionPaintsEntireRow = false;
 const bool PlatformStyle::kTreeViewUsesOpenIcon = true;
 const bool PlatformStyle::kUseRipples = true;
 const bool PlatformStyle::kMirrorBubbleArrowInRTLByDefault = true;
+const bool PlatformStyle::kTextfieldScrollsToStartOnFocusChange = false;
 
 // static
 std::unique_ptr<ScrollBar> PlatformStyle::CreateScrollBar(bool is_horizontal) {

ui/views/style/platform_style.h

@@ -66,6 +66,10 @@ class VIEWS_EXPORT PlatformStyle {
   // opens in the opposite direction.
   static const bool kMirrorBubbleArrowInRTLByDefault;
 
+  // Whether to scroll text fields to the beginning when they gain or lose
+  // focus.
+  static const bool kTextfieldScrollsToStartOnFocusChange;
+
   // Creates the default scrollbar for the given orientation.
   static std::unique_ptr<ScrollBar> CreateScrollBar(bool is_horizontal);
 

ui/views/style/platform_style_mac.mm

@@ -20,6 +20,7 @@ const bool PlatformStyle::kDefaultLabelButtonHasBoldFont = false;
 const bool PlatformStyle::kDialogDefaultButtonCanBeCancel = false;
 const bool PlatformStyle::kSelectWordOnRightClick = true;
 const bool PlatformStyle::kSelectAllOnRightClickWhenUnfocused = true;
+const bool PlatformStyle::kTextfieldScrollsToStartOnFocusChange = true;
 const bool PlatformStyle::kTreeViewSelectionPaintsEntireRow = true;
 const bool PlatformStyle::kTreeViewUsesOpenIcon = false;
 const bool PlatformStyle::kUseRipples = false;