RenderTextHarfBuzz: Add support for multi line text selection.

ui/views/examples/label_example.cc

Index: ui/views/examples/label_example.cc
diff --git a/ui/views/examples/label_example.cc b/ui/views/examples/label_example.cc
index 4255e71679c88747698b89989ab2573d26977be9..0b6b344c3663237c289319208d8381dc1cbb1712 100644
--- a/ui/views/examples/label_example.cc
+++ b/ui/views/examples/label_example.cc
@@ -132,6 +132,8 @@ void LabelExample::ButtonPressed(Button* button, const ui::Event& event) {
       shadows.push_back(gfx::ShadowValue(gfx::Vector2d(2, 2), 0, SK_ColorGRAY));
     }
     custom_label_->SetShadows(shadows);
+  } else if (button == text_selection_) {
+    custom_label_->SetSelectable(text_selection_->checked());
   }
   custom_label_->parent()->parent()->Layout();
   custom_label_->SchedulePaint();
@@ -186,6 +188,8 @@ void LabelExample::AddCustomLabel(View* container) {
                         0, GridLayout::USE_PREF, 0, 0);
   column_set->AddColumn(GridLayout::LEADING, GridLayout::LEADING,
                         0, GridLayout::USE_PREF, 0, 0);
+  column_set->AddColumn(GridLayout::LEADING, GridLayout::LEADING, 0,
+                        GridLayout::USE_PREF, 0, 0);
   layout->StartRow(0, 1);
   multiline_ = new Checkbox(base::ASCIIToUTF16("Multiline"));
   multiline_->set_listener(this);
@@ -193,6 +197,9 @@ void LabelExample::AddCustomLabel(View* container) {
   shadows_ = new Checkbox(base::ASCIIToUTF16("Shadows"));
   shadows_->set_listener(this);
   layout->AddView(shadows_);
+  text_selection_ = new Checkbox(base::ASCIIToUTF16("Text selection"));

[msw, 2016/12/07 20:20:35]

nit: rename the identifier |selectable_| and change this string to "Selectable"

[karandeepb, 2016/12/12 10:36:19]

Done.

+  text_selection_->set_listener(this);
+  layout->AddView(text_selection_);
   layout->AddPaddingRow(0, 8);
 
   column_set = layout->AddColumnSet(2);
@@ -205,6 +212,13 @@ void LabelExample::AddCustomLabel(View* container) {
   custom_label_->SetText(textfield_->text());
   layout->AddView(custom_label_);
 
+  // Disable the text selection checkbox if |custom_label_| does not support
+  // text selection.
+  if (custom_label_->SetSelectable(true))
+    text_selection_->SetChecked(true);

[msw, 2016/12/07 20:20:35]

Don't set selectable and check by default, just disable the checkbox if
!custom_label_->IsSelectionSupported() instead

[karandeepb, 2016/12/12 10:36:19]

Done. This required making Label::IsSelectionSupported public, which sort of
makes sense.

+  else
+    text_selection_->SetEnabled(false);
+
   container->AddChildView(control_container);
 }