Revert "Make UTF16RagelIterator::operator*() to use DCHECK() instead of CHECK()"

This reverts commit d7878194.

Reason for revert: [Sheriff] blink_platform_unittests fails on Cast Audio Linux bot.
Sample failure: https://ci.chromium.org/p/chromium/builders/ci/Cast%20Audio%20Linux/50660

Original change's description:
> Make UTF16RagelIterator::operator*() to use DCHECK() instead of CHECK()
> 
> This patch changes |UTF16RagelIterator::operator*()| to use |DCHECK()| instead
> of |CHECK()| for improving performance because this function is called many
> times as number of characters in the page.
> 
> In text heavy page, I observe 12% speed up.
> 
> Change-Id: I5febb53f0f096b3bd76e6330a70b6464b9cb4758
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1760846
> Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
> Commit-Queue: Dominik Röttsches <drott@chromium.org>
> Reviewed-by: Dominik Röttsches <drott@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#688476}

TBR=yosin@chromium.org,eae@chromium.org,drott@chromium.org

Change-Id: If3d54ab8ae171d55be5f989c3e7d4fccf254d9fa
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1761279Reviewed-by: Marina Ciocea <marinaciocea@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688480}

third_party/blink/renderer/platform/fonts/utf16_ragel_iterator.h

@@ -106,7 +106,7 @@ class PLATFORM_EXPORT UTF16RagelIterator {
   }
 
   UChar32 operator*() {
-    DCHECK(buffer_size_);
+    CHECK(buffer_size_);
     return cached_category_;
   }