Strip anonymous blocks when change in style removes need for them

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index 6032af9af5a0375b784178fdb93eec83740789cf..9c4f14519a50bc2d8bf0bdd74475ed490ec03905 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -110,6 +110,8 @@ static DelayedUpdateScrollInfoSet* gDelayedUpdateScrollInfoSet = 0;
 
 static bool gColumnFlowSplitEnabled = true;
 
+static bool s_noLongerAffectsParentBlock = false;

[esprehn, 2014/05/06 18:55:44]

This should be a member of RenderBlock like the other static bits.

+
 // This class helps dispatching the 'overflow' event on layout change. overflow can be set on RenderBoxes, yet the existing code
 // only works on RenderBlocks. If this changes, this class should be shared with other RenderBoxes.
 class OverflowEventDispatcher {
@@ -308,6 +310,10 @@ void RenderBlock::styleWillChange(StyleDifference diff, const RenderStyle& newSt
         }
     }
 
+    s_noLongerAffectsParentBlock = !isFloatingOrOutOfFlowPositioned()

[Julien - ping for review, 2014/05/07 01:38:46]

RenderObject has a static boolean called s_affectsParentBlock, are those
related?

+        && (newStyle.isFloating() || newStyle.hasOutOfFlowPosition())
+        && parent() && parent()->isRenderBlockFlow();
+
     RenderBox::styleWillChange(diff, newStyle);
 }
 
@@ -329,6 +335,9 @@ void RenderBlock::styleDidChange(StyleDifference diff, const RenderStyle* oldSty
 {
     RenderBox::styleDidChange(diff, oldStyle);
 
+    if (s_noLongerAffectsParentBlock)

[ojan, 2014/05/06 18:43:02]

Why do you need the static? Can't you do the check in styleWillChange here
instead?

+        toRenderBlock(parent())->removeAnonymousWrappersIfRequired();
+
     RenderStyle* newStyle = style();
 
     if (!isAnonymousBlock()) {
@@ -1052,6 +1061,31 @@ static bool canMergeContiguousAnonymousBlocks(RenderObject* oldChild, RenderObje
            && prev->isAnonymousColumnSpanBlock() == next->isAnonymousColumnSpanBlock();
 }
 
+bool RenderBlock::canRemoveAnonymousWrappers()
+{
+    for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {

[Julien - ping for review, 2014/05/07 01:38:46]

You seem to care only about blocks so we should probably just walk our box
children.

Better even, don't have a children walk here.

+        if (!child->isAnonymousBlock() && !child->isFloatingOrOutOfFlowPositioned())
+            return false;
+        if (child->isRenderBlock() && toRenderBlock(child)->continuation())
+            return false;
+    }
+    return true;
+}
+
+void RenderBlock::removeAnonymousWrappersIfRequired()
+{
+    if (!canRemoveAnonymousWrappers())
+        return;
+
+    RenderObject* child = firstChild();
+    while (child) {

[Julien - ping for review, 2014/05/07 01:38:46]

Same comment about walking boxes (ideally blocks but we don't have them).

+        RenderObject* next = child->nextSibling();
+        if (child->isAnonymousBlock())
+            collapseAnonymousBlockChild(this, toRenderBlock(child));
+        child = next;

[Julien - ping for review, 2014/05/07 01:38:46]

I would put a comment here as this is important:

// WARNING: |child| is destroyed here.

+    }
+}
+
 void RenderBlock::collapseAnonymousBlockChild(RenderBlock* parent, RenderBlock* child)
 {
     // It's possible that this block's destruction may have been triggered by the