Scrollbar ThumbLength is not updated when window size is changed.

cc/layers/painted_scrollbar_layer.cc

 // Copyright 2013 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/painted_scrollbar_layer.h"
 
 #include "base/auto_reset.h"
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
 #include "cc/layers/painted_scrollbar_layer_impl.h"
@@ skipping 23 matching lines @@
 }
 
 PaintedScrollbarLayer::PaintedScrollbarLayer(scoped_ptr<Scrollbar> scrollbar,
                                              int scroll_layer_id)
     : scrollbar_(scrollbar.Pass()),
       scroll_layer_id_(scroll_layer_id),
       clip_layer_id_(Layer::INVALID_ID),
       thumb_thickness_(scrollbar_->ThumbThickness()),
       thumb_length_(scrollbar_->ThumbLength()),
       is_overlay_(scrollbar_->IsOverlay()),
-      has_thumb_(scrollbar_->HasThumb()) {
+      has_thumb_(scrollbar_->HasThumb()),
+      cache_has_thumb_(false) {
   if (!scrollbar_->IsOverlay())
     SetShouldScrollOnMainThread(true);
 }
 
 PaintedScrollbarLayer::~PaintedScrollbarLayer() {}
 
 int PaintedScrollbarLayer::ScrollLayerId() const {
   return scroll_layer_id_;
 }
 
@@ skipping 127 matching lines @@
         gfx::Size(scrollbar_->ThumbThickness(), scrollbar_->ThumbLength());
   }
   return gfx::Rect(thumb_size);
 }
 
 void PaintedScrollbarLayer::UpdateThumbAndTrackGeometry() {
   UpdateProperty(scrollbar_->TrackRect(), &track_rect_);
   UpdateProperty(scrollbar_->Location(), &location_);
   UpdateProperty(scrollbar_->IsOverlay(), &is_overlay_);
   UpdateProperty(scrollbar_->HasThumb(), &has_thumb_);
-  if (has_thumb_) {
+  if ((cache_has_thumb_ != has_thumb_) || has_thumb_) {

[danakj, 2014/09/03 15:38:27]

I mean you don't need to add this cache_has_thumb_. I don't want to add a member
variable to this class when we don't need to.

When has_thumb_ is false, just UpdateProperty(0, &thumb_thickness_); etc. no? Or
just remove the if(has_thumb) if the ThumbLength() function does the right thing
already?

     UpdateProperty(scrollbar_->ThumbThickness(), &thumb_thickness_);
     UpdateProperty(scrollbar_->ThumbLength(), &thumb_length_);
+    cache_has_thumb_ = has_thumb_;
   }
 }
 
 bool PaintedScrollbarLayer::Update(ResourceUpdateQueue* queue,
                                    const OcclusionTracker<Layer>* occlusion) {
   UpdateThumbAndTrackGeometry();
 
   gfx::Rect track_layer_rect = gfx::Rect(location_, bounds());
   gfx::Rect scaled_track_rect = ScrollbarLayerRectToContentRect(
       track_layer_rect);
@@ skipping 58 matching lines @@
 
   scrollbar_->PaintPart(&skcanvas, part, layer_rect);
   // Make sure that the pixels are no longer mutable to unavoid unnecessary
   // allocation and copying.
   skbitmap.setImmutable();
 
   return UIResourceBitmap(skbitmap);
 }
 
 }  // namespace cc