Don't calculate a shown ratio when top controls height is 0.

cc/input/top_controls_manager_unittest.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/input/top_controls_manager.h"
 
 #include <algorithm>
+#include <cmath>
 
+#include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "cc/input/top_controls_manager_client.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/test/fake_impl_proxy.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
 #include "cc/test/test_shared_bitmap_manager.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/frame_time.h"
@@ skipping 25 matching lines @@
   void DidChangeTopControlsPosition() override {
     redraw_needed_ = true;
     update_draw_properties_needed_ = true;
   }
 
   bool HaveRootScrollLayer() const override { return true; }
 
   float TopControlsHeight() const override { return top_controls_height_; }
 
   void SetCurrentTopControlsShownRatio(float ratio) override {
+    ASSERT_FALSE(std::isnan(ratio));
+    ASSERT_FALSE(ratio == std::numeric_limits<float>::infinity());
+    ASSERT_FALSE(ratio == -std::numeric_limits<float>::infinity());
     ratio = std::max(ratio, 0.f);
     ratio = std::min(ratio, 1.f);
     top_controls_shown_ratio_ = ratio;
   }
 
   float CurrentTopControlsShownRatio() const override {
     return top_controls_shown_ratio_;
   }
 
   LayerImpl* rootScrollLayer() {
@@ skipping 374 matching lines @@
   EXPECT_FALSE(manager->animation());
   EXPECT_FLOAT_EQ(-50.f, manager->ControlsTopOffset());
   EXPECT_FLOAT_EQ(0.f, manager->ContentTopOffset());
 
   client.SetTopControlsHeight(0.f);
   EXPECT_FALSE(manager->animation());
   EXPECT_FLOAT_EQ(0.f, manager->ControlsTopOffset());
   EXPECT_FLOAT_EQ(0.f, manager->ContentTopOffset());
 }
 
+TEST(TopControlsManagerTest, ScrollByWithZeroHeightControlsIsNoop) {
+  MockTopControlsManagerClient client(0.f, 0.5f, 0.5f);
+  TopControlsManager* manager = client.manager();
+  manager->UpdateTopControlsState(BOTH, BOTH, false);
+
+  manager->ScrollBegin();
+  gfx::Vector2dF pending = manager->ScrollBy(gfx::Vector2dF(0.f, 20.f));
+  EXPECT_FLOAT_EQ(20.f, pending.y());
+  EXPECT_FLOAT_EQ(0.f, manager->ControlsTopOffset());
+  EXPECT_FLOAT_EQ(0.f, manager->ContentTopOffset());
+  EXPECT_FLOAT_EQ(1.f, client.CurrentTopControlsShownRatio());
+  manager->ScrollEnd();
+}
+
+
 }  // namespace
 }  // namespace cc