Widget opacity goes from 0 to 1, not 0 to 255.

cc/layers/layer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 449 matching lines @@
 void Layer::SetBackgroundFilters(const FilterOperations& filters) {
   DCHECK(IsPropertyChangeAllowed());
   if (background_filters_ == filters)
     return;
   background_filters_ = filters;
   SetNeedsCommit();
 }
 
 void Layer::SetOpacity(float opacity) {
   DCHECK(IsPropertyChangeAllowed());
+  DCHECK_GE(opacity, 0.f);
+  DCHECK_LE(opacity, 1.f);
+
   if (opacity_ == opacity)
     return;
   // We need to force a property tree rebuild when opacity changes from 1 to a
   // non-1 value or vice-versa as render surfaces can change.
   bool force_rebuild = opacity == 1.f || opacity_ == 1.f;
   opacity_ = opacity;
   SetSubtreePropertyChanged();
   if (layer_tree_host_ && !force_rebuild) {
     PropertyTrees* property_trees = layer_tree_host_->property_trees();
     auto effect_id_to_index = property_trees->effect_id_to_index_map.find(id());
@@ skipping 1126 matching lines @@
 
 // On<Property>Animated is called due to an ongoing accelerated animation.
 // Since this animation is also being run on the compositor thread, there
 // is no need to request a commit to push this value over, so the value is
 // set directly rather than by calling Set<Property>.
 void Layer::OnFilterAnimated(const FilterOperations& filters) {
   filters_ = filters;
 }
 
 void Layer::OnOpacityAnimated(float opacity) {
+  DCHECK_GE(opacity, 0.f);
+  DCHECK_LE(opacity, 1.f);
+
   if (opacity_ == opacity)
     return;
   opacity_ = opacity;
   // Changing the opacity may make a previously hidden layer visible, so a new
   // recording may be needed.
   SetNeedsUpdate();
   if (layer_tree_host_) {
     PropertyTrees* property_trees = layer_tree_host_->property_trees();
     if (property_trees->IsInIdToIndexMap(PropertyTrees::TreeType::EFFECT,
                                          id())) {
@@ skipping 198 matching lines @@
       ->data.num_copy_requests_in_subtree;
 }
 
 gfx::Transform Layer::screen_space_transform() const {
   DCHECK_NE(transform_tree_index_, -1);
   return draw_property_utils::ScreenSpaceTransform(
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 }  // namespace cc