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

ui/views/controls/scroll_view_unittest.cc

Index: ui/views/controls/scroll_view_unittest.cc
diff --git a/ui/views/controls/scroll_view_unittest.cc b/ui/views/controls/scroll_view_unittest.cc
index f91d0bd73c1e3bdfefe2cedadfce56756fa7a3b7..ceb28b5fb7030a1370fcb26efedb7edb8d3c687c 100644
--- a/ui/views/controls/scroll_view_unittest.cc
+++ b/ui/views/controls/scroll_view_unittest.cc
@@ -869,6 +869,40 @@ TEST_F(ScrollViewTest, ConstrainScrollToBounds) {
   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.