Scroll the position into view when the content is not visible.

Previously, we implement scrollIntoView by scrolling the intersection of the viewport and the content. However, when the content is not visible in the viewport, e.g. outside boundary and the viewport's overflow attribute is hidden, the intersection would be empty and the browser would stop the scrolling logic. In this case, we presume the webpage wants to scroll the position of the content but for some reason doesn't want to show it. In this patch, we scroll the content's position for this special case. BUG=673396 CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2 Review-Url: https://codereview.chromium.org/2576963002 Cr-Commit-Position: refs/heads/master@{#441469}

Scroll the position into view when the content is not visible.
Previously, we implement scrollIntoView by scrolling the intersection of the viewport and the content. However, when the content is not visible in the viewport, e.g. outside boundary and the viewport's overflow attribute is hidden, the intersection would be empty and the browser would stop the scrolling logic. In this case, we presume the webpage wants to scroll the position of the content but for some reason doesn't want to show it. In this patch, we scroll the content's position for this special case. BUG=673396 CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2 Review-Url: https://codereview.chromium.org/2576963002 Cr-Commit-Position: refs/heads/master@{#441469}
961e2d02 · sunyunjia · Commit bot · 38c3c8c8 · 961e2d02 · 961e2d02
Commit 961e2d02 authored Jan 04, 2017 by sunyunjia Committed by Commit bot Jan 04, 2017
2 changed files
--- a/third_party/WebKit/LayoutTests/fast/scrolling/scroll-into-view-hidden-element.html
+++ b/third_party/WebKit/LayoutTests/fast/scrolling/scroll-into-view-hidden-element.html
+<!DOCTYPE html>
+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<div style="height: 2000px"></div>
+<div style="overflow: scroll; height: 100px">
+  <div id="scroll" style="margin-top: -15px; height: 15px; width: 15px;background-color: red"></div>
+  Target
+</div>
+<script>
+test(function(t) {
+  var scroll = document.getElementById("scroll");
+  scroll.scrollIntoView();
+  assert_not_equals(window.scrollY, 0);
+}, "Tests that when the element to be scrolled can't be scrolled to visible in its closest scrollable parent, the element's position should still be scrolled into view");
+</script>
\ No newline at end of file
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -85,6 +85,12 @@

 namespace blink {

+static LayoutRect localToAbsolute(LayoutBox& offset, LayoutRect rect) {
+  return LayoutRect(
+      offset.localToAbsoluteQuad(FloatQuad(FloatRect(rect)), UseTransforms)
+          .boundingBox());
+}
+
 PaintLayerScrollableAreaRareData::PaintLayerScrollableAreaRareData() {}

 const int ResizerControlExpandRatioForTouch = 2;
@@ -1622,25 +1628,17 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
  ScrollOffset oldScrollOffset = getScrollOffset();
  ScrollOffset newScrollOffset(clampScrollOffset(roundedIntSize(
      toScrollOffset(FloatPoint(r.location()) + oldScrollOffset))));
-
-  if (newScrollOffset == oldScrollOffset) {
-    return LayoutRect(
-        box()
-            .localToAbsoluteQuad(FloatQuad(FloatRect(intersection(
-                                     layerBounds, localExposeRect))),
-                                 UseTransforms)
-            .boundingBox());
-  }
-
  setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
  ScrollOffset scrollOffsetDifference = getScrollOffset() - oldScrollOffset;
  localExposeRect.move(-LayoutSize(scrollOffsetDifference));
-  return LayoutRect(
-      box()
-          .localToAbsoluteQuad(
-              FloatQuad(FloatRect(intersection(layerBounds, localExposeRect))),
-              UseTransforms)
-          .boundingBox());
+
+  LayoutRect intersect =
+      localToAbsolute(box(), intersection(layerBounds, localExposeRect));
+  if (intersect.isEmpty() && !layerBounds.isEmpty() &&
+      !localExposeRect.isEmpty()) {
+    return localToAbsolute(box(), localExposeRect);
+  }
+  return intersect;
 }

 void PaintLayerScrollableArea::updateScrollableAreaSet(bool hasOverflow) {