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()),
+      has_thumb_pre_(false) {

[Sikugu_, 2014/09/01 14:46:19]

can we have some better name here like cache_thumb_value_?

   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 ((has_thumb_ != has_thumb_pre_) || has_thumb_) {

[danakj, 2014/09/02 16:23:06]

I don't understand, when has_thumb_ became false, you still want to update it?
But you don't have a thumb anymore.

[MuVen, 2014/09/02 16:42:04]

When "Pin it" is clicked a pop-up of window height of 367 and content height of
451 is created, during that time has_thumb_ is true, but later bec of some js
window height is increased to 451.
When window height is increased to 451 has_thumb_ is false, and thumb_length
should be zero. As has_thumb_ is false UpdateProperty on thumb_length_ is not
updated to 0 
(which is 202 previously).

[danakj, 2014/09/02 18:38:55]

Ok, then how about when has_thumb is false, we always UpdateProperty of these 2
things to 0?

Also can you please add unit tests for this.

[MuVen, 2014/09/03 07:04:39]

When has_thumb is false, UpdateProperty of ThumbLength() is calculated @
ScrollbarTheme::thumbLength().If ScrollBar is disabled Length will be 0. Test
Case is added.

     UpdateProperty(scrollbar_->ThumbThickness(), &thumb_thickness_);
     UpdateProperty(scrollbar_->ThumbLength(), &thumb_length_);
+    has_thumb_pre_ = 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