Strip anonymous wrappers when a block flow no longer requires them

Source/core/layout/LayoutBlock.cpp

Index: Source/core/layout/LayoutBlock.cpp
diff --git a/Source/core/layout/LayoutBlock.cpp b/Source/core/layout/LayoutBlock.cpp
index 272ce512f78950e1eb1368b7cd47f9fbc454c5f9..86db6cd30a8c1287139c724058741c230bb1009c 100644
--- a/Source/core/layout/LayoutBlock.cpp
+++ b/Source/core/layout/LayoutBlock.cpp
@@ -271,8 +271,14 @@ void LayoutBlock::styleDidChange(StyleDifference diff, const ComputedStyle* oldS
 {
     LayoutBox::styleDidChange(diff, oldStyle);
 
-    if (isFloatingOrOutOfFlowPositioned() && oldStyle && !oldStyle->isFloating() && !oldStyle->hasOutOfFlowPosition() && parent() && parent()->isLayoutBlockFlow())
+    if (isFloatingOrOutOfFlowPositioned() && oldStyle && !oldStyle->isFloating() && !oldStyle->hasOutOfFlowPosition() && parent() && parent()->isLayoutBlockFlow()) {
         toLayoutBlock(parent())->removeAnonymousWrappersIfRequired();
+        // Reparent to an adjacent anonymous block if one is available.
+        if (previousSibling() && previousSibling()->isAnonymousBlock())
+            toLayoutBlock(parent())->moveChildTo(toLayoutBlock(previousSibling()), this, 0, false);
+        if (nextSibling() && nextSibling()->isAnonymousBlock())
+            toLayoutBlock(parent())->moveChildTo(toLayoutBlock(nextSibling()), this, nextSibling()->slowFirstChild(), false);
+    }
 
     const ComputedStyle& newStyle = styleRef();
 
@@ -376,6 +382,17 @@ void LayoutBlock::invalidateDisplayItemClients(const LayoutBoxModelObject& paint
     invalidateDisplayItemClientForStartOfContinuationsIfNeeded(*this);
 }
 
+void LayoutBlock::addAdjacentSiblingsToAnonymousBox(AdjacentSiblings siblings, LayoutBlock* anonymousBox)
+{
+    bool previousSiblings = siblings == PreviousSiblings;
+    LayoutObject* child = previousSiblings ? anonymousBox->previousSibling() : anonymousBox->nextSibling();
+    while (child && child->isFloatingOrOutOfFlowPositioned()) {
+        LayoutObject* sibling = previousSiblings ? child->previousSibling() : child->nextSibling();
+        moveChildTo(anonymousBox, child, previousSiblings ? anonymousBox->firstChild() : 0, false);
+        child = sibling;
+    }
+}
+
 void LayoutBlock::addChildIgnoringContinuation(LayoutObject* newChild, LayoutObject* beforeChild)
 {
     if (beforeChild && beforeChild->parent() != this) {
@@ -439,17 +456,36 @@ void LayoutBlock::addChildIgnoringContinuation(LayoutObject* newChild, LayoutObj
         // it is put into an anomyous block box. We try to use an existing anonymous box if possible, otherwise
         // a new one is created and inserted into our list of children in the appropriate position.
         LayoutObject* afterChild = beforeChild ? beforeChild->previousSibling() : lastChild();
-
         if (afterChild && afterChild->isAnonymousBlock()) {
             afterChild->addChild(newChild);
             return;
         }
 
+        // If we are a block that allows inline children and the child we're adding means that

[mstensho (USE GERRIT), 2015/09/07 14:01:47]

But we are not a block that allows inline children.

We're inside "if (!childrenInline() && ...)".

How do we end up with !childrenInline() and only floating or out-of-flow
children? I think that's a bug.

+        // we can now treat all children as inline without the need for anonymous blocks, then do that.
+        LayoutObject* nextChild = firstChild();
+        bool childrenAllInline = !isFlexibleBoxIncludingDeprecated() && !isLayoutGrid();
+        while (nextChild && childrenAllInline) {
+            if (!nextChild->isFloatingOrOutOfFlowPositioned()) {
+                childrenAllInline = false;
+                break;
+            }
+            nextChild = nextChild->nextSibling();
+        }
+        if (childrenAllInline) {
+            LayoutBox::addChild(newChild, beforeChild);
+            setChildrenInline(true);
+            return;
+        }
+
         if (newChild->isInline()) {
             // No suitable existing anonymous box - create a new one.
             LayoutBlock* newBox = createAnonymousBlock();
             LayoutBox::addChild(newBox, beforeChild);
+            // Reparent adjacent inline siblings to the new box.
+            addAdjacentSiblingsToAnonymousBox(PreviousSiblings, newBox);
             newBox->addChild(newChild);
+            addAdjacentSiblingsToAnonymousBox(NextSiblings, newBox);
             return;
         }
     }