Add extra DCHECKing to try to catch subpixel rendering on a non-opaque

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 ada76779cfc7875a48d4f39dda80919f9bd11761..c596b98afb57ed69f14dd2bd5c28ba55e80abfec 100644
--- a/ui/views/controls/label.cc
+++ b/ui/views/controls/label.cc
@@ -450,8 +450,30 @@ std::unique_ptr<gfx::RenderText> Label::CreateRenderText(
 
 void Label::PaintText(gfx::Canvas* canvas) {
   MaybeBuildRenderTextLines();
+
   for (size_t i = 0; i < lines_.size(); ++i)
     lines_[i]->Draw(canvas);
+
+#if DCHECK_IS_ON()
+  if (!lines_.empty()) {

[sadrul, 2017/02/08 02:13:56]

early return insrtead

[Evan Stade, 2017/02/11 00:18:07]

Done.

+    // Attempt to ensure that if we're using subpixel rendering, we're painting
+    // to an opaque background. What we don't want to find is an ancestor in the
+    // hierarchy that paints to a non-opaque layer.
+    if (!lines_[0]->subpixel_rendering_suppressed()) {

[sadrul, 2017/02/08 02:13:56]

ditto

[Evan Stade, 2017/02/11 00:18:07]

Done.

+      for (View* view = this; view; view = view->parent()) {
+        if (view->background())

[sadrul, 2017/02/08 02:13:56]

Maybe you can continue with the loop if
SkColorGetA(view->background()->get_color()) != OPAQUE or something.

[Evan Stade, 2017/02/11 00:18:07]

Done.

+          break;
+        if (view->layer()) {
+          DCHECK(view->layer()->fills_bounds_opaquely())
+              << " Ancestor view has a non-opaque layer: "
+              << view->GetClassName() << " with ID " << view->id();
+          break;
+        }
+      }
+    }
+  }
+#endif
+
 }
 
 void Label::OnBoundsChanged(const gfx::Rect& previous_bounds) {
@@ -979,7 +1001,8 @@ void Label::RecalculateColors() {
 void Label::ApplyTextColors() const {
   SkColor color = enabled() ? actual_enabled_color_ : actual_disabled_color_;
   bool subpixel_rendering_suppressed =
-      SkColorGetA(background_color_) != 0xFF || !subpixel_rendering_enabled_;
+      SkColorGetA(background_color_) != SK_AlphaOPAQUE ||
+      !subpixel_rendering_enabled_;
   for (size_t i = 0; i < lines_.size(); ++i) {
     lines_[i]->SetColor(color);
     lines_[i]->set_selection_color(actual_selection_text_color_);