RenderTextHarfBuzz: Add support for multi line text selection.

ui/views/controls/label_unittest.cc

Index: ui/views/controls/label_unittest.cc
diff --git a/ui/views/controls/label_unittest.cc b/ui/views/controls/label_unittest.cc
index e8fa4f95826e023d4e6d235e6fba9b914a11d2cb..cf74d57ea1cd797a1ba8e8e287d54892ad570766 100644
--- a/ui/views/controls/label_unittest.cc
+++ b/ui/views/controls/label_unittest.cc
@@ -820,13 +820,9 @@ TEST_F(LabelSelectionTest, Selectable) {
   ASSERT_TRUE(label()->SetSelectable(true));
   EXPECT_TRUE(label()->selectable());
 
-  // Verify that making a label multiline causes the label to not support text
+  // Verify that making a label multiline still causes the label to support text
   // selection.
   label()->SetMultiLine(true);
-  EXPECT_FALSE(label()->selectable());
-
-  label()->SetMultiLine(false);
-  ASSERT_TRUE(label()->SetSelectable(true));
   EXPECT_TRUE(label()->selectable());
 
   // Verify that obscuring the label text causes the label to not support text