Add infrastructure for partial layouts

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 5c7a9d90b55bb66764259d87e17aec1720eae4fe..71eb228dae13e927f8af09245741fb5fb99127c1 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -1407,6 +1407,9 @@ void RenderBlock::layout()
     // layoutBlock().
     layoutBlock(false);
 
+    if (document()->view()->canStopPartialLayout())
+        return;
+
     // It's safe to check for control clip here, since controls can never be table cells.
     // If we have a lightweight clip, there can never be any overflow from children.
     if (hasControlClip() && m_overflow)
@@ -1537,6 +1540,8 @@ void RenderBlock::checkForPaginationLogicalHeightChange(LayoutUnit& pageLogicalH
 void RenderBlock::layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalHeight)
 {
     ASSERT(needsLayout());
+//    if (document()->view()->canStopPartialLayout())
+//        return;
 
     if (isInline() && !isInlineBlockOrInlineTable()) // Inline <form>s inside various table elements can
         return;                                      // cause us to come in here.  Just bail.
@@ -1600,6 +1605,12 @@ void RenderBlock::layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalHeigh
     else
         layoutBlockChildren(relayoutChildren, maxFloatLogicalBottom);
 
+    // If layout was just for one of our children, stop early (before setting setNeedsLayout=false!)
+    if (document()->view()->canStopPartialLayout()) {
+        statePusher.pop();
+        return;
+    }
+
     // Expand our intrinsic height to encompass floats.
     LayoutUnit toAdd = borderAfter() + paddingAfter() + scrollbarLogicalHeight();
     if (lowestFloatLogicalBottom() > (logicalHeight() - toAdd) && expandsToEncloseOverhangingFloats())
@@ -1647,6 +1658,9 @@ void RenderBlock::layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalHeigh
 
     fitBorderToLinesIfNeeded();
 
+    if (document()->view()->canStopPartialLayout())
+        return;
+
     if (renderView->layoutState()->m_pageLogicalHeight)
         setPageLogicalOffset(renderView->layoutState()->pageLogicalOffset(this, logicalTop()));
 
@@ -2519,6 +2533,10 @@ void RenderBlock::layoutBlockChildren(bool relayoutChildren, LayoutUnit& maxFloa
 
         // Lay out the child.
         layoutBlockChild(child, marginInfo, previousFloatLogicalBottom, maxFloatLogicalBottom);
+
+        document()->view()->checkPartialLayoutComplete(child);
+        if (document()->view()->canStopPartialLayout())
+            break;
     }
 
     // Now do the handling of the bottom of the block, adding in our bottom border/padding and
@@ -2583,6 +2601,9 @@ void RenderBlock::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo, Lay
     if (childNeededLayout)
         child->layout();
 
+    if (document()->view()->canStopPartialLayout())
+        return;
+
     // Cache if we are at the top of the block right now.
     bool atBeforeSideOfBlock = marginInfo.atBeforeSideOfBlock();