Add more tracing information for troubleshooting

Add TRACE calls to scroll related methods to help with troubleshooting.
TRACE the following methods: ScrollTree::SetScrollOffset,
ScrollTree::OnScrollOffsetAnimated, ScrollableArea::ScrollOffsetChanged.

Bug: 1087088
Change-Id: If0b29816aa7092041f071e6c9b72941105581e52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2288288
Commit-Queue: Liviu Tinta <liviutinta@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786923}

cc/trees/property_tree.cc

@@ -1292,6 +1292,8 @@ void ScrollTree::OnScrollOffsetAnimated(ElementId id,
   if (!property_trees()->is_active)
     return;
 
+  TRACE_EVENT2("cc", "ScrollTree::OnScrollOffsetAnimated", "x",
+               scroll_offset.x(), "y", scroll_offset.y());
   ScrollNode* scroll_node = Node(scroll_tree_index);
   if (SetScrollOffset(id,
                       ClampScrollOffsetToLimits(scroll_offset, *scroll_node)))
@@ -1589,6 +1591,9 @@ void ScrollTree::SetBaseScrollOffset(ElementId id,
 
 bool ScrollTree::SetScrollOffset(ElementId id,
                                  const gfx::ScrollOffset& scroll_offset) {
+  // TODO(crbug.com/1087088): Remove TRACE_EVENT call when the bug is fixed
+  TRACE_EVENT2("cc", "ScrollTree::SetScrollOffset", "x", scroll_offset.x(), "y",
+               scroll_offset.y());
   if (property_trees()->is_main_thread) {
     if (scroll_offset_map_[id] == scroll_offset)
       return false;

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

@@ -376,7 +376,10 @@ PhysicalRect ScrollableArea::ScrollIntoView(
 
 void ScrollableArea::ScrollOffsetChanged(const ScrollOffset& offset,
                                          mojom::blink::ScrollType scroll_type) {
-  TRACE_EVENT0("blink", "ScrollableArea::scrollOffsetChanged");
+  TRACE_EVENT2("input", "ScrollableArea::scrollOffsetChanged", "x",
+               offset.Width(), "y", offset.Height());
+  TRACE_EVENT_INSTANT1("input", "Type", TRACE_EVENT_SCOPE_THREAD, "type",
+                       scroll_type);
 
   ScrollOffset old_offset = GetScrollOffset();
   ScrollOffset truncated_offset = ShouldUseIntegerScrollOffset()