Begin tracking why layout is invalidated

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 2d121fb69f1912c3f578143fcd885360efd71e21..97e32046d0545f5cb50310fe1acfdd176df6acb9 100644
--- a/Source/core/layout/LayoutBlock.cpp
+++ b/Source/core/layout/LayoutBlock.cpp
@@ -718,9 +718,9 @@ void LayoutBlock::splitFlow(LayoutObject* beforeChild, LayoutBlock* newBlockBox,
     // Always just do a full layout in order to ensure that line boxes (especially wrappers for images)
     // get deleted properly.  Because objects moves from the pre block into the post block, we want to
     // make new line boxes instead of leaving the old line boxes around.
-    pre->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
-    block->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
-    post->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
+    pre->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
+    block->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
+    post->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
 }
 
 void LayoutBlock::makeChildrenAnonymousColumnBlocks(LayoutObject* beforeChild, LayoutBlockFlow* newBlockBox, LayoutObject* newChild)
@@ -768,10 +768,10 @@ void LayoutBlock::makeChildrenAnonymousColumnBlocks(LayoutObject* beforeChild, L
     // get deleted properly.  Because objects moved from the pre block into the post block, we want to
     // make new line boxes instead of leaving the old line boxes around.
     if (pre)
-        pre->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
-    block->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
+        pre->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
+    block->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
     if (post)
-        post->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
+        post->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
 }
 
 LayoutBlockFlow* LayoutBlock::columnsBlockForSpanningElement(LayoutObject* newChild)
@@ -1122,7 +1122,7 @@ void LayoutBlock::collapseAnonymousBlockChild(LayoutBlock* parent, LayoutBlock*
     // destroyed. See crbug.com/282088
     if (child->beingDestroyed())
         return;
-    parent->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
+    parent->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ChildAnonymousBlockChanged);
     parent->setChildrenInline(child->childrenInline());
     LayoutObject* nextSibling = child->nextSibling();
 
@@ -1162,7 +1162,7 @@ void LayoutBlock::removeChild(LayoutObject* oldChild)
     LayoutObject* next = oldChild->nextSibling();
     bool canMergeAnonymousBlocks = canMergeContiguousAnonymousBlocks(oldChild, prev, next);
     if (canMergeAnonymousBlocks && prev && next) {
-        prev->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
+        prev->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::AnonymousBlockChange);
         LayoutBlockFlow* nextBlock = toLayoutBlockFlow(next);
         LayoutBlockFlow* prevBlock = toLayoutBlockFlow(prev);
 
@@ -1184,7 +1184,7 @@ void LayoutBlock::removeChild(LayoutObject* oldChild)
             // Now just put the inlineChildrenBlock inside the blockChildrenBlock.
             blockChildrenBlock->children()->insertChildNode(blockChildrenBlock, inlineChildrenBlock, prev == inlineChildrenBlock ? blockChildrenBlock->firstChild() : 0,
                 inlineChildrenBlockHasLayer || blockChildrenBlock->hasLayer());
-            next->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation();
+            next->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::AnonymousBlockChange);
 
             // inlineChildrenBlock got reparented to blockChildrenBlock, so it is no longer a child
             // of "this". we null out prev or next so that is not used later in the function.
@@ -1730,7 +1730,7 @@ void LayoutBlock::layoutPositionedObjects(bool relayoutChildren, PositionedLayou
         // FIXME: We should be able to do a r->setNeedsPositionedMovementLayout() here instead of a full layout. Need
         // to investigate why it does not trigger the correct invalidations in that case. crbug.com/350756
         if (info == ForcedLayoutAfterContainingBlockMoved)
-            r->setNeedsLayout(MarkOnlyThis);
+            r->setNeedsLayout(LayoutInvalidationReason::AncestorMoved, MarkOnlyThis);

[esprehn, 2015/03/23 20:19:43]

Just like with setNeedsStyleRecalc I'd prefer the argument for "reason" was
last. The enums and class name are so long it pushes the important part of the
code way off to the side.

[pdr., 2015/03/24 03:56:18]

setNeedsLayout takes 2 optional arguments so if we put the reason last, all
callsites will need to list the default values for the optional arguments.

An option is to introduce two different versions of these functions:
void setNeedsLayout(LayoutInvalidationReasonForTracing reason) {
setNeedsLayout([default marking behavior], [default layout scope], reason); }
void setNeedsLayout(MarkingBehavior, SubtreeLayoutScope*,
LayoutInvalidationReasonForTracing)

I think this makes the code more confusing than the argument order. If possible
I'd like to avoid making the reason optional which will force callers of
setNeedsLayout to keep the reasons up to date. Any other ideas?

 
         r->layoutIfNeeded();