RenderTextHarfBuzz: Add support for multi line text selection.

ui/views/controls/label.cc

Index: ui/views/controls/label.cc
diff --git a/ui/views/controls/label.cc b/ui/views/controls/label.cc
index ce7ee0247b2e31a48edf9f62d90025d62f4eb350..9b04c091ff1ab436580068f0d8a18cb0e9526562 100644
--- a/ui/views/controls/label.cc
+++ b/ui/views/controls/label.cc
@@ -175,8 +175,6 @@ void Label::SetMultiLine(bool multi_line) {
   if (render_text_->MultilineSupported())
     render_text_->SetMultiline(multi_line);
   render_text_->SetReplaceNewlineCharsWithSymbols(!multi_line);
-  if (multi_line)
-    SetSelectable(false);
   ResetLayout();
 }
 
@@ -250,7 +248,7 @@ base::string16 Label::GetDisplayTextForTesting() {
 }
 
 bool Label::IsSelectionSupported() const {
-  return !multi_line() && !obscured() && render_text_->IsSelectionSupported();
+  return !obscured() && render_text_->IsSelectionSupported();
 }
 
 bool Label::SetSelectable(bool value) {