AXPosition: Promoting two DCHECKs to CHECK in order to debug a crash in the field

No information as to how to reproduce the linked bug has been provided in the crash reports.
Therefore, using two CHECKs as a quick way of gathering more information from the field.

TBR=dmazzoni@chromium.org, aleventhal@chromium.org

Bug: 1022601
Change-Id: Id7ef83bc58e0b41a16f8a0a7df1720c7f2470618
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1948495Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721141}

ui/accessibility/ax_position.h

@@ -1594,9 +1594,10 @@ class AXPosition {
     if (!text_position->IsIgnored() && !text_position->AtStartOfAnchor()) {
       std::unique_ptr<base::i18n::BreakIterator> grapheme_iterator =
           text_position->GetGraphemeIterator();
-      DCHECK_GE(text_position->text_offset_, 0);
-      DCHECK_LE(text_position->text_offset_,
-                int{text_position->name_.length()});
+      CHECK_GE(text_position->text_offset_, 0) << *this << '\n' << name_;
+      CHECK_LE(text_position->text_offset_, int{text_position->name_.length()})
+          << *this << '\n'
+          << name_;
       while (
           !text_position->AtEndOfAnchor() &&
           (!gfx::IsValidCodePointIndex(text_position->name_,