Fix the DCHECK failure in render_text_harfbuzz.cc.

ui/gfx/render_text_harfbuzz.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/render_text_harfbuzz.h"
 
 #include <limits>
 #include <set>
 
 #include "base/i18n/bidi_line_iterator.h"
@@ skipping 386 matching lines @@
   // that belong to the same run.
   void AddLineSegment(const internal::LineSegment& segment) {
     DCHECK(!lines_.empty());
     internal::Line* line = &lines_.back();
     const internal::TextRunHarfBuzz& run = *(run_list_.runs()[segment.run]);
     if (!line->segments.empty()) {
       internal::LineSegment& last_segment = line->segments.back();
       // Merge segments that belong to the same run.
       if (last_segment.run == segment.run) {
         DCHECK_EQ(last_segment.char_range.end(), segment.char_range.start());
-        DCHECK_LE(
-            std::abs(last_segment.x_range.end() - segment.x_range.start()),
-            std::numeric_limits<float>::epsilon());

[msw, 2016/05/04 22:03:59]

It seems like there's likely floating math rounding errors somewhere (failing on
3.05176e-05 vs. 1.19209e-07). I think it's still a useful DCHECK if we just
change it to check that the difference is less than 1.0f (ie. there's less than
a pixel between one run and the next)? They really should be equal, but checking
<1.0f is better than nothing at all. WDYT?

[xdai1, 2016/05/04 22:49:46]

I agree with you. Thanks for your suggestion!

         last_segment.char_range.set_end(segment.char_range.end());
         last_segment.x_range.set_end(SkScalarToFloat(text_x_) +
                                      segment.width());
         if (run.is_rtl && last_segment.char_range.end() == run.range.end())
           UpdateRTLSegmentRanges();
         line->size.set_width(line->size.width() + segment.width());
         text_x_ += segment.width();
         available_width_ -= segment.width();
         return;
       }
@@ skipping 1160 matching lines @@
   DCHECK(!update_layout_run_list_);
   DCHECK(!update_display_run_list_);
   return text_elided() ? display_run_list_.get() : &layout_run_list_;
 }
 
 const internal::TextRunList* RenderTextHarfBuzz::GetRunList() const {
   return const_cast<RenderTextHarfBuzz*>(this)->GetRunList();
 }
 
 }  // namespace gfx