Scrollbar ThumbLength is not updated, when window size is changed.

When a pop-up is opened the window size is 367 and content size is 451
and scrollbar of thumblength 202 is created. Pop-Window height has been
resized to 451 because of JS . Before resizing of Pop-Window scrollbar
thumb_length of 202 is been applied. After resizing Pop-Window vertical
scrollbar is disabled during UpdateScrollbarGeometry(has_thumb_ = false).

Now When PaintedScrollbarLayer::UpdateThumbAndTrackGeometry is called
after pop-up window resize, as has_thumb_ = false , UpdateProperty on
thumb_length_ is not applied, due to which we are seeing the unwanted
scrollbar

BUG=400136

Review URL: https://codereview.chromium.org/524373003

Cr-Commit-Position: refs/heads/master@{#293218}

3 files changed, 48 insertions, 0 deletions

diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index c0b2a72..7062bc1 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -192,6 +192,9 @@ void PaintedScrollbarLayer::UpdateThumbAndTrackGeometry() {
   if (has_thumb_) {
     UpdateProperty(scrollbar_->ThumbThickness(), &thumb_thickness_);
     UpdateProperty(scrollbar_->ThumbLength(), &thumb_length_);
+  } else {
+    UpdateProperty(0, &thumb_thickness_);
+    UpdateProperty(0, &thumb_length_);
   }
 }
 
diff --git a/cc/layers/scrollbar_layer_unittest.cc b/cc/layers/scrollbar_layer_unittest.cc
index bcec55a..4c5e5b4 100644
--- a/cc/layers/scrollbar_layer_unittest.cc
+++ b/cc/layers/scrollbar_layer_unittest.cc
@@ -192,6 +192,50 @@ TEST(PaintedScrollbarLayerTest, ScrollOffsetSynchronization) {
     scrollbar_layer_impl->ScrollbarParametersDidChange();           \
   } while (false)
 
+TEST(ScrollbarLayerTest, UpdatePropertiesOfScrollBarWhenThumbRemoved) {
+  scoped_ptr<FakeLayerTreeHost> host = FakeLayerTreeHost::Create();
+  scoped_refptr<Layer> root_clip_layer = Layer::Create();
+  scoped_refptr<Layer> root_layer = Layer::Create();
+  scoped_refptr<Layer> content_layer = Layer::Create();
+  scoped_refptr<FakePaintedScrollbarLayer> scrollbar_layer =
+      FakePaintedScrollbarLayer::Create(false, true, root_layer->id());
+
+  root_layer->SetScrollClipLayerId(root_clip_layer->id());
+  // Give the root-clip a size that will result in MaxScrollOffset = (80, 0).
+  root_clip_layer->SetBounds(gfx::Size(20, 50));
+  root_layer->SetBounds(gfx::Size(100, 50));
+  content_layer->SetBounds(gfx::Size(100, 50));
+
+  host->SetRootLayer(root_clip_layer);
+  root_clip_layer->AddChild(root_layer);
+  root_layer->AddChild(content_layer);
+  root_layer->AddChild(scrollbar_layer);
+
+  root_layer->SetScrollOffset(gfx::Vector2d(0, 0));
+  scrollbar_layer->SetBounds(gfx::Size(70, 10));
+  scrollbar_layer->SetScrollLayer(root_layer->id());
+  scrollbar_layer->SetClipLayer(root_clip_layer->id());
+  scrollbar_layer->fake_scrollbar()->set_location(gfx::Point(20, 10));
+  scrollbar_layer->fake_scrollbar()->set_track_rect(gfx::Rect(30, 10, 50, 10));
+  scrollbar_layer->fake_scrollbar()->set_thumb_thickness(10);
+  scrollbar_layer->fake_scrollbar()->set_thumb_length(4);
+
+  scrollbar_layer->UpdateThumbAndTrackGeometry();
+  LayerImpl* root_clip_layer_impl = NULL;
+  LayerImpl* root_layer_impl = NULL;
+  PaintedScrollbarLayerImpl* scrollbar_layer_impl = NULL;
+
+  UPDATE_AND_EXTRACT_LAYER_POINTERS();
+  EXPECT_EQ(gfx::Rect(10, 0, 4, 10).ToString(),
+            scrollbar_layer_impl->ComputeThumbQuadRect().ToString());
+
+  scrollbar_layer->fake_scrollbar()->set_has_thumb(false);
+
+  UPDATE_AND_EXTRACT_LAYER_POINTERS();
+  EXPECT_EQ(gfx::Rect(10, 0, 0, 0).ToString(),
+            scrollbar_layer_impl->ComputeThumbQuadRect().ToString());
+}
+
 TEST(ScrollbarLayerTest, ThumbRect) {
   scoped_ptr<FakeLayerTreeHost> host = FakeLayerTreeHost::Create();
   scoped_refptr<Layer> root_clip_layer = Layer::Create();
diff --git a/cc/test/fake_scrollbar.h b/cc/test/fake_scrollbar.h
index 872b9d9..8e6d454 100644
--- a/cc/test/fake_scrollbar.h
+++ b/cc/test/fake_scrollbar.h
@@ -36,6 +36,7 @@ class FakeScrollbar : public Scrollbar {
       thumb_thickness_ = thumb_thickness;
   }
   void set_thumb_length(int thumb_length) { thumb_length_ = thumb_length; }
+  void set_has_thumb(bool has_thumb) { has_thumb_ = has_thumb; }
   SkColor paint_fill_color() const { return SK_ColorBLACK | fill_color_; }
 
  private: