Cherry-pick WebKit r100677 to fix a rendering crash

This fixes a crash from positioned generated content under run-in.
See http://trac.webkit.org/changeset/100677.

Bug: 6079158
Change-Id: I3d2012c58f47e71ae500e33551dfab5587b84534
diff --git a/Source/WebCore/rendering/RenderBlock.cpp b/Source/WebCore/rendering/RenderBlock.cpp
index 373523d..a90bf69 100644
--- a/Source/WebCore/rendering/RenderBlock.cpp
+++ b/Source/WebCore/rendering/RenderBlock.cpp
@@ -1561,6 +1561,16 @@
 
     RenderBlock* currBlock = toRenderBlock(curr);
 
+    // First we destroy any :before/:after content. It will be regenerated by the new inline.
+    // Exception is if the run-in itself is generated.
+    if (child->style()->styleType() != BEFORE && child->style()->styleType() != AFTER) {
+        RenderObject* generatedContent;
+        if (child->getCachedPseudoStyle(BEFORE) && (generatedContent = child->beforePseudoElementRenderer()))
+            generatedContent->destroy();
+        if (child->getCachedPseudoStyle(AFTER) && (generatedContent = child->afterPseudoElementRenderer()))
+            generatedContent->destroy();
+    }
+
     // Remove the old child.
     children()->removeChildNode(this, blockRunIn);
 
@@ -1569,16 +1579,11 @@
     RenderInline* inlineRunIn = new (renderArena()) RenderInline(runInNode ? runInNode : document());
     inlineRunIn->setStyle(blockRunIn->style());
 
-    bool runInIsGenerated = child->style()->styleType() == BEFORE || child->style()->styleType() == AFTER;
-
-    // Move the nodes from the old child to the new child, but skip any :before/:after content.  It has already
-    // been regenerated by the new inline.
+    // Move the nodes from the old child to the new child
     for (RenderObject* runInChild = blockRunIn->firstChild(); runInChild;) {
         RenderObject* nextSibling = runInChild->nextSibling();
-        if (runInIsGenerated || (runInChild->style()->styleType() != BEFORE && runInChild->style()->styleType() != AFTER)) {
-            blockRunIn->children()->removeChildNode(blockRunIn, runInChild, false);
-            inlineRunIn->addChild(runInChild); // Use addChild instead of appendChildNode since it handles correct placement of the children relative to :after-generated content.
-        }
+        blockRunIn->children()->removeChildNode(blockRunIn, runInChild, false);
+        inlineRunIn->addChild(runInChild); // Use addChild instead of appendChildNode since it handles correct placement of the children relative to :after-generated content.
         runInChild = nextSibling;
     }