Scrollbar ThumbLength is not updated when window size is changed.

cc/layers/painted_scrollbar_layer.cc

Index: cc/layers/painted_scrollbar_layer.cc
diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index c0b2a728e3c9077c46a7f194dce94174d0780fd0..84624d6a04801d4e06e4a83c6ec1e0871fbd6595 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -41,7 +41,8 @@ PaintedScrollbarLayer::PaintedScrollbarLayer(scoped_ptr<Scrollbar> scrollbar,
       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);
 }
@@ -189,9 +190,10 @@ void PaintedScrollbarLayer::UpdateThumbAndTrackGeometry() {
   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_;
   }
 }