Tentatively change TextIterator to CHECK clean layout, instead of DCHECK

This patch changes the DCHECK of clean layout in TextIterator to CHECK,
so that we can catch remaining lifecycle issues.

Bug: 739060
Change-Id: I0ee0a152b438d3d8e1f97de0acd2844b190ef703
Reviewed-on: https://chromium-review.googlesource.com/575597Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487454}

third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp

@@ -200,9 +200,9 @@ TextIteratorAlgorithm<Strategy>::TextIteratorAlgorithm(
   // TODO(dglazkov): TextIterator should not be created for documents that don't
   // have a frame, but it currently still happens in some cases. See
   // http://crbug.com/591877 for details.
-  DCHECK(!start.GetDocument()->View() ||
-         !start.GetDocument()->View()->NeedsLayout());
-  DCHECK(!start.GetDocument()->NeedsLayoutTreeUpdate());
+  CHECK(!start.GetDocument()->View() ||
+        !start.GetDocument()->View()->NeedsLayout());
+  CHECK(!start.GetDocument()->NeedsLayoutTreeUpdate());
   // To avoid renderer hang, we use |CHECK_LE()| to catch the bad callers
   // in release build.
   CHECK_LE(start, end);