Don't reset scroll position of contents on every ScrollView layout.

ui/views/controls/scroll_view_unittest.cc

 // Copyright (c) 2012 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 "ui/views/controls/scroll_view.h"
 
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ skipping 851 matching lines @@
   EXPECT_EQ(fully_scrolled.x(), test_api.CurrentOffset().x());
 
   // And 77 pixels wider should scroll left. Also make it short again: the y-
   // offset from the last change should remain.
   scroll_view_.SetBoundsRect(gfx::Rect(0, 0, 177, 100));
   scroll_view_.Layout();
   EXPECT_EQ(fully_scrolled.y() - 55, test_api.CurrentOffset().y());
   EXPECT_EQ(fully_scrolled.x() - 77, test_api.CurrentOffset().x());
 }
 
+// Calling Layout on ScrollView should not reset the scroll location.
+TEST_F(ScrollViewTest, ContentScrollNotResetOnLayout) {
+  ScrollViewTestApi test_api(&scroll_view_);
+
+  CustomView* contents = new CustomView;
+  contents->SetPreferredSize(gfx::Size(300, 300));
+  scroll_view_.SetContents(contents);
+  scroll_view_.ClipHeightTo(0, 150);
+  scroll_view_.SizeToPreferredSize();
+  // ScrollView preferred width matches that of |contents|, with the height
+  // capped at the value we clipped to.
+  EXPECT_EQ(gfx::Size(300, 150), scroll_view_.size());
+
+  // Scroll down.
+  scroll_view_.ScrollToPosition(
+      const_cast<ScrollBar*>(scroll_view_.vertical_scroll_bar()), 25);
+  EXPECT_EQ(25, test_api.CurrentOffset().y());
+  // Call Layout; no change to scroll position.
+  scroll_view_.Layout();
+  EXPECT_EQ(25, test_api.CurrentOffset().y());
+  // Change contents of |contents|, call Layout; still no change to scroll
+  // position.
+  contents->SetPreferredSize(gfx::Size(300, 500));
+  contents->InvalidateLayout();
+  scroll_view_.Layout();
+  EXPECT_EQ(25, test_api.CurrentOffset().y());
+
+  // Change |contents| to be shorter than the ScrollView's clipped height.
+  // This /will/ change the scroll location due to ConstrainScrollToBounds.
+  contents->SetPreferredSize(gfx::Size(300, 50));
+  scroll_view_.Layout();
+  EXPECT_EQ(0, test_api.CurrentOffset().y());
+}
+
 // Test scrolling behavior when clicking on the scroll track.
 TEST_F(WidgetScrollViewTest, ScrollTrackScrolling) {
   // Set up with a vertical scroller.
   ScrollView* scroll_view =
       AddScrollViewWithContentSize(gfx::Size(10, kDefaultHeight * 5));
   ScrollViewTestApi test_api(scroll_view);
   BaseScrollBar* scroll_bar = test_api.GetBaseScrollBar(VERTICAL);
   View* thumb = test_api.GetScrollBarThumb(VERTICAL);
 
   // Click in the middle of the track, ensuring it's below the thumb.
@@ skipping 105 matching lines @@
   // Scroll via ScrollView API. Should be reflected on the impl side.
   offset.set_y(kDefaultHeight * 4);
   scroll_view->contents()->ScrollRectToVisible(offset);
   EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), test_api.CurrentOffset());
 
   EXPECT_TRUE(compositor->GetScrollOffsetForLayer(layer_id, &impl_offset));
   EXPECT_EQ(gfx::ScrollOffset(0, offset.y()), impl_offset);
 }
 
 }  // namespace views