Adjust scroll animation on clamping scroll, rather than just setting scroll.

This allows a clamping scroll to correctly fix scroll animations from
a previous scroll anchoring animation.

Bug: 1026985

Change-Id: Ic39dc466c596cc601040454c86d0a310bd241419
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929439
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718843}

third_party/blink/renderer/core/layout/scroll_anchor_test.cc

@@ -4,6 +4,7 @@
 
 #include "third_party/blink/renderer/core/layout/scroll_anchor.h"
 
+#include "build/build_config.h"
 #include "third_party/blink/renderer/core/dom/static_node_list.h"
 #include "third_party/blink/renderer/core/frame/root_frame_viewport.h"
 #include "third_party/blink/renderer/core/frame/visual_viewport.h"
@@ -11,6 +12,7 @@
 #include "third_party/blink/renderer/core/layout/layout_box.h"
 #include "third_party/blink/renderer/core/page/print_context.h"
 #include "third_party/blink/renderer/core/paint/paint_layer_scrollable_area.h"
+#include "third_party/blink/renderer/core/scroll/scroll_animator_base.h"
 #include "third_party/blink/renderer/core/testing/core_unit_test_helper.h"
 #include "third_party/blink/renderer/platform/testing/histogram_tester.h"
 #include "third_party/blink/renderer/platform/testing/runtime_enabled_features_test_helpers.h"
@@ -927,4 +929,43 @@ TEST_P(ScrollAnchorTest, DeleteAnonymousBlockCrash) {
   GetDocument().getElementById("deleteMe")->remove();
   Update();
 }
+
+TEST_P(ScrollAnchorTest, ClampAdjustsAnchorAnimation) {
+  SetBodyInnerHTML(R"HTML(
+    <style>
+      body { margin: 0 }
+      .content {
+        height: 45vh;
+        background: lightblue;
+      }
+      #hidden {
+        height: 200px;
+        display: none;
+      }
+    </style>
+    <div class="content" id=one></div>
+    <div id="hidden"></div>
+    <div class="content" id=two></div>
+    <div class="content" id=three></div>
+    <div class="content" id=four></div>
+  )HTML");
+  LayoutViewport()->SetScrollOffset(ScrollOffset(0, 2000), kUserScroll);
+  Update();
+  GetDocument().getElementById("hidden")->setAttribute(html_names::kStyleAttr,
+                                                       "display:block");
+  GetDocument().UpdateStyleAndLayout();
+#if !defined(OS_MACOSX)
+  EXPECT_EQ(IntSize(0, 200), LayoutViewport()
+                                 ->GetScrollAnimator()
+                                 .ImplOnlyAnimationAdjustmentForTesting());
+#endif
+  GetDocument().getElementById("hidden")->setAttribute(html_names::kStyleAttr,
+                                                       "");
+  GetDocument().UpdateStyleAndLayout();
+  // The clamping scroll after resizing layout overflow to be smaller
+  // should adjust the animation back to 0.
+  EXPECT_EQ(IntSize(0, 0), LayoutViewport()
+                               ->GetScrollAnimator()
+                               .ImplOnlyAnimationAdjustmentForTesting());
+}
 }

third_party/blink/renderer/core/scroll/scroll_animator_compositor_coordinator.h

@@ -170,6 +170,7 @@ class CORE_EXPORT ScrollAnimatorCompositorCoordinator
                            UserScrollCallBackAtAnimationFinishOnMainThread);
   FRIEND_TEST_ALL_PREFIXES(ScrollAnimatorTest,
                            UserScrollCallBackAtAnimationFinishOnCompositor);
+  FRIEND_TEST_ALL_PREFIXES(ScrollAnchorTest, ClampAdjustsAnchorAnimation);
 
   std::unique_ptr<CompositorAnimation> compositor_animation_;
   // The element id to which the compositor animation is attached when

third_party/blink/renderer/core/scroll/scrollable_area.cc

@@ -238,9 +238,12 @@ void ScrollableArea::SetScrollOffset(const ScrollOffset& offset,
 
   switch (scroll_type) {
     case kCompositorScroll:
-    case kClampingScroll:
       ScrollOffsetChanged(clamped_offset, scroll_type);
       break;
+    case kClampingScroll:
+      GetScrollAnimator().AdjustAnimationAndSetScrollOffset(clamped_offset,
+                                                            scroll_type);
+      break;
     case kAnchoringScroll:
       GetScrollAnimator().AdjustAnimationAndSetScrollOffset(clamped_offset,
                                                             scroll_type);