Don't clamp scroll positions until the end of all layouts

third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp b/third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp
index 994c3a841ac2a9dd41442d2b243e4f41e50156b1..7c43f5024cf49a0a7038fca7ce12044eaf5021d3 100644
--- a/third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp
@@ -288,8 +288,13 @@ void LayoutFlexibleBox::layoutBlock(bool relayoutChildren)
 
         layoutFlexItems(relayoutChildren, layoutScope);
 
-        if (LayoutBlock::finishDelayUpdateScrollInfo(&layoutScope))
+        ScrollPositionMap scrollMap;
+        if (LayoutBlock::finishDelayUpdateScrollInfo(&layoutScope, &scrollMap)) {

[leviw_travelin_and_unemployed, 2016/04/01 18:05:10]

The lack of a test makes me a sad panda.

It seems like we're only storing one level deep here. If the flexboxes are
nested, the first pass of the inner flexbox, if smaller, will still lose its
position. Does that make sense? 

Why doesn't the map need the same lifetime as gDelayUpdateScrollInfo (storing
the initial values in the first pass and updating them only when we're
finished)?

             layoutFlexItems(false, layoutScope);
+            for (auto& entry : scrollMap) {
+                entry.key->scrollToPosition(entry.value);
+            }
+        }
 
         if (logicalHeight() != previousHeight)
             relayoutChildren = true;