[Editing][BugFix] Fix if condition in ReplaceSelectionCommand

third_party/WebKit/Source/core/editing/commands/ReplaceSelectionCommand.cpp

 /*
  * Copyright (C) 2005, 2006, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2009, 2010, 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 995 matching lines @@
         insertionPos = endingSelection().start();
     }
 
     // We don't want any of the pasted content to end up nested in a Mail blockquote, so first break
     // out of any surrounding Mail blockquotes. Unless we're inserting in a table, in which case
     // breaking the blockquote will prevent the content from actually being inserted in the table.
     if (startIsInsideMailBlockquote && m_preventNesting && !(enclosingNodeOfType(insertionPos, &isTableStructureNode))) {
         applyCommandToComposite(BreakBlockquoteCommand::create(document()));
         // This will leave a br between the split.
         Node* br = endingSelection().start().anchorNode();
-        ASSERT(isHTMLBRElement(br));
-        // Insert content between the two blockquotes, but remove the br (since it was just a placeholder).
-        insertionPos = positionInParentBeforeNode(*br);
-        removeNode(br);
+        if (isHTMLBRElement(br)) {

[yosin_UTC9, 2015/10/15 05:57:18]

It seems this can fix issue 541402 too. However, issue 541402, root cause
of this assertion failure is different. Can we make BreakBlockquoteCommand
always to insert BR?

What BreakBlockquoteCommand fail to insert BR?

+            // Insert content between the two blockquotes, but remove the br (since it was just a placeholder).
+            insertionPos = positionInParentBeforeNode(*br);
+            removeNode(br);
+        }
     }
 
     // Inserting content could cause whitespace to collapse, e.g. inserting <div>foo</div> into hello^ world.
     prepareWhitespaceAtPositionForSplit(insertionPos);
 
     // If the downstream node has been removed there's no point in continuing.
     if (!mostForwardCaretPosition(insertionPos).anchorNode())
         return;
 
     // NOTE: This would be an incorrect usage of downstream() if downstream() were changed to mean the last position after
@@ skipping 519 matching lines @@
 DEFINE_TRACE(ReplaceSelectionCommand)
 {
     visitor->trace(m_startOfInsertedContent);
     visitor->trace(m_endOfInsertedContent);
     visitor->trace(m_insertionStyle);
     visitor->trace(m_documentFragment);
     CompositeEditCommand::trace(visitor);
 }
 
 } // namespace blink