Add ability to underline links on hover in Views

ui/views/controls/link.cc

Index: ui/views/controls/link.cc
diff --git a/ui/views/controls/link.cc b/ui/views/controls/link.cc
index d116aa35db5f74e8039bae56162a6b42fe34ee0a..5909629fc7898ca841e0e1fe3748e9419199b0bd 100644
--- a/ui/views/controls/link.cc
+++ b/ui/views/controls/link.cc
@@ -94,6 +94,16 @@ void Link::OnMouseCaptureLost() {
   SetPressed(false);
 }
 
+void Link::OnMouseEntered(const ui::MouseEvent& event) {
+  mouse_inside_ = true;
+  RecalculateFont();
+}
+
+void Link::OnMouseExited(const ui::MouseEvent& event) {
+  mouse_inside_ = false;
+  RecalculateFont();
+}
+
 bool Link::OnKeyPressed(const ui::KeyEvent& event) {
   bool activate = ((event.key_code() == ui::VKEY_SPACE) ||
                    (event.key_code() == ui::VKEY_RETURN));
@@ -156,6 +166,11 @@ void Link::SetPressedColor(SkColor color) {
     Label::SetEnabledColor(requested_pressed_color_);
 }
 
+void Link::SetUnderlineOnHover(bool underline_on_hover) {
+  underline_on_hover_ = underline_on_hover;
+  RecalculateFont();
+}
+
 void Link::Init() {
   static bool initialized = false;
   static SkColor kDefaultEnabledColor;
@@ -178,6 +193,8 @@ void Link::Init() {
 
   listener_ = NULL;
   pressed_ = false;
+  underline_on_hover_ = false;
+  mouse_inside_ = false;
   SetEnabledColor(kDefaultEnabledColor);
   SetDisabledColor(kDefaultDisabledColor);
   SetPressedColor(kDefaultPressedColor);
@@ -196,8 +213,15 @@ void Link::SetPressed(bool pressed) {
 }
 
 void Link::RecalculateFont() {
-  // The font should be underlined iff the link is enabled.
-  if (enabled() == !(font().GetStyle() & gfx::Font::UNDERLINED)) {
+  if (underline_on_hover_) {
+    // For underline on hover, the font should be underlined iff the link is
+    // enabled and the mouse is hovering over it.
+    Label::SetFont(font().DeriveFont(0, enabled() && mouse_inside_ ?
+        (font().GetStyle() | gfx::Font::UNDERLINED) :
+        (font().GetStyle() & ~gfx::Font::UNDERLINED)));
+  } else if (enabled() == !(font().GetStyle() & gfx::Font::UNDERLINED)) {
+    // For constant underlining, the font should be underlined iff the link is
+    // enabled.
     Label::SetFont(font().DeriveFont(0, enabled() ?
         (font().GetStyle() | gfx::Font::UNDERLINED) :
         (font().GetStyle() & ~gfx::Font::UNDERLINED)));