Remove obsolete float-management code from line layout

Source/core/layout/LayoutBlockFlowLine.cpp

Index: Source/core/layout/LayoutBlockFlowLine.cpp
diff --git a/Source/core/layout/LayoutBlockFlowLine.cpp b/Source/core/layout/LayoutBlockFlowLine.cpp
index 18c10cce7a561db99e71d25bfbf7224085246241..10fccd480b97973d8f1c7dd4506544f620fea671 100644
--- a/Source/core/layout/LayoutBlockFlowLine.cpp
+++ b/Source/core/layout/LayoutBlockFlowLine.cpp
@@ -38,7 +38,6 @@
 #include "core/layout/line/LayoutTextInfo.h"
 #include "core/layout/line/LineLayoutState.h"
 #include "core/layout/line/LineWidth.h"
-#include "core/layout/line/TrailingFloatsRootInlineBox.h"
 #include "core/layout/line/WordMeasurement.h"
 #include "core/layout/svg/line/SVGRootInlineBox.h"
 #include "platform/fonts/Character.h"
@@ -816,7 +815,6 @@ void LayoutBlockFlow::layoutRunsAndFloatsInRange(LineLayoutState& layoutState,
             // Once BidiRunList is separated from BidiResolver this will not be needed.
             resolver.runs().deleteRuns();
             resolver.markCurrentRunEmpty(); // FIXME: This can probably be replaced by an ASSERT (or just removed).
-            layoutState.setCheckForFloatsFromLastLine(true);
             resolver.setPosition(InlineIterator(resolver.position().root(), 0, 0), 0);
             break;
         }
@@ -1012,7 +1010,7 @@ void LayoutBlockFlow::linkToEndLineIfNeeded(LineLayoutState& layoutState)
         }
     }
 
-    if (m_floatingObjects && (layoutState.checkForFloatsFromLastLine() || positionNewFloats()) && lastRootBox()) {
+    if (positionNewFloats() && lastRootBox()) {
         // In case we have a float on the last line, it might not be positioned up to now.
         // This has to be done before adding in the bottom border/padding, or the float will
         // include the padding incorrectly. -dwh
@@ -1030,22 +1028,6 @@ void LayoutBlockFlow::linkToEndLineIfNeeded(LineLayoutState& layoutState)
         if (it == end)
             return;
 
-        if (layoutState.checkForFloatsFromLastLine()) {
-            LayoutUnit bottomVisualOverflow = lastRootBox()->logicalBottomVisualOverflow();
-            LayoutUnit bottomLayoutOverflow = lastRootBox()->logicalBottomLayoutOverflow();
-            TrailingFloatsRootInlineBox* trailingFloatsLineBox = new TrailingFloatsRootInlineBox(*this);
-            m_lineBoxes.appendLineBox(trailingFloatsLineBox);
-            trailingFloatsLineBox->setConstructed();
-            GlyphOverflowAndFallbackFontsMap textBoxDataMap;
-            VerticalPositionCache verticalPositionCache;
-            LayoutUnit blockLogicalHeight = logicalHeight();
-            trailingFloatsLineBox->alignBoxesInBlockDirection(blockLogicalHeight, textBoxDataMap, verticalPositionCache);
-            trailingFloatsLineBox->setLineTopBottomPositions(blockLogicalHeight, blockLogicalHeight, blockLogicalHeight, blockLogicalHeight);
-            LayoutRect logicalLayoutOverflow(0, blockLogicalHeight, 1, bottomLayoutOverflow - blockLogicalHeight);
-            LayoutRect logicalVisualOverflow(0, blockLogicalHeight, 1, bottomVisualOverflow - blockLogicalHeight);
-            trailingFloatsLineBox->setOverflowFromLogicalRects(logicalLayoutOverflow, logicalVisualOverflow, trailingFloatsLineBox->lineTop(), trailingFloatsLineBox->lineBottom());
-        }
-
         for (; it != end; ++it)
             appendFloatingObjectToLastLine(*it->get());
     }
@@ -1546,6 +1528,7 @@ void LayoutBlockFlow::layoutInlineChildren(bool relayoutChildren, LayoutUnit& pa
         // deleted and only dirtied. In that case, we can layout the replaced
         // elements at the same time.
         Vector<LayoutBox*> replacedChildren;
+        LayoutObject* lastChild = nullptr;
         for (InlineWalker walker(this); !walker.atEnd(); walker.advance()) {
             LayoutObject* o = walker.current();
 
@@ -1580,7 +1563,13 @@ void LayoutBlockFlow::layoutInlineChildren(bool relayoutChildren, LayoutUnit& pa
                     dirtyLineBoxesForObject(o, layoutState.isFullLayout());
                 o->clearNeedsLayout();
             }
+            if (!o->isText() || !toLayoutText(o)->isAllCollapsibleWhitespace())
+                lastChild = o;
         }
+        // If there is a trailing float on the line that will possibly occur after a natural line break
+        // then dirty its adjacent lineboxes to ensure it gets placed.

[leviw_travelin_and_unemployed, 2015/07/28 18:25:38]

If it's the last child and a float, will we ever be dirtying more than one
linebox?

[rhogan, 2015/07/28 19:10:37]

The one it's on and possibly the one before it. There would be no line boxes
after it obviously.

+        if (lastChild && lastChild->isFloating())
+            dirtyLinesFromChangedChild(lastChild);

[leviw_travelin_and_unemployed, 2015/07/28 18:25:38]

Where did we dirty these lines before?

[rhogan, 2015/07/28 19:10:37]

We didn't. Instead we added a new line box at the end of the block and placed
the float there, even though it wasn't a 'new' one. This allowed us to overwrite
the 'originatingLine' that the float uses to track the linebox it sits in. It
also left an unnecessary linebox sitting around before it.

My change, instead of relying on this layoutState.checkForFloatsFromLastLine()
check, instead gets rid of the linebox the float is attached to so that
positionNewFloats() returns true, i.e. we're placing a new float and have to
find a linebox for it. That allows us to add it to its linebox in
appendFloatingObjectToLastLine() in the new line 1032 above and overwrite the
'originatingLine' it stores.

I think this also leaves us with fewer unnecessary lineboxes in this scenario.
(The test case is trailing-float.html)

 
         for (size_t i = 0; i < replacedChildren.size(); i++)
             replacedChildren[i]->layoutIfNeeded();