Get rid of false assert from CompositeEditCommand::moveParagraphContentsToNewBlockIfNecessary

Source/core/editing/CompositeEditCommand.cpp

Index: Source/core/editing/CompositeEditCommand.cpp
diff --git a/Source/core/editing/CompositeEditCommand.cpp b/Source/core/editing/CompositeEditCommand.cpp
index b208a812a939821643de0d856ac23f6fe6332393..3fd79137735d67b11dab93e8febf0f183284dfc4 100644
--- a/Source/core/editing/CompositeEditCommand.cpp
+++ b/Source/core/editing/CompositeEditCommand.cpp
@@ -923,9 +923,6 @@ PassRefPtr<Node> CompositeEditCommand::moveParagraphContentsToNewBlockIfNecessar
                 return nullptr;
             }
         } else if (enclosingBlock(upstreamEnd.deprecatedNode()) != upstreamStart.deprecatedNode()) {
-            // The visibleEnd.  It must be an ancestor of the paragraph start.
-            // We can bail as we have a full block to work with.
-            ASSERT(upstreamStart.deprecatedNode()->isDescendantOf(enclosingBlock(upstreamEnd.deprecatedNode())));

[Yuta Kitamura, 2014/05/28 09:14:10]

I tried to follow the code but couldn't understand why
this deletion is safe... Could you give a bit more context,
please?

[yosin_UTC9, 2014/05/29 04:04:39]

My reasoning is rather simple. We have a case breaking this ASSERT. The author
who add this ASSERT didn't consider empty list but visible.

[Yuta Kitamura, 2014/05/29 09:00:24]

I thought about this for some time but I couldn't reach the conclusion
that this ASSERT is bogus; it looks like a legit assumption to me.

Rather, I think there's something wrong in positions creation logic in
lines 896-900, because it's weird that |upstreamStart| and |upstreamEnd|
belong to different paragraphs.

[Yuta Kitamura, 2014/05/30 04:40:45]

I started to feel like this ASSERT is indeed bogus.

So I'm fine with removing the ASSERT, but could you un-delete the portion
of the comment explaining this "if" condition? It looks useful. (I'm okay
with removing the text "The visibleEnd." which does not make any sense
to me.)

[yosin_UTC9, 2014/05/30 05:04:26]

Done.

             return nullptr;
         } else if (isEndOfEditableOrNonEditableContent(visibleEnd)) {
             // At the end of the editable region. We can bail here as well.