Don't add Segoe UI to the fallback font list if it is the system font.

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 "base/i18n/bidi_line_iterator.h"
 #include "base/i18n/break_iterator.h"
 #include "base/i18n/char_iterator.h"
 #include "base/profiler/scoped_tracker.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/trace_event/trace_event.h"
 #include "third_party/harfbuzz-ng/src/hb.h"
 #include "third_party/icu/source/common/unicode/ubidi.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkTypeface.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/font_fallback.h"
 #include "ui/gfx/font_render_params.h"
 #include "ui/gfx/geometry/safe_integer_conversions.h"
@@ skipping 1266 matching lines @@
         GetFallbackFontFamilies(uniscribe_family);
     fallback_families.insert(fallback_families.end(),
         uniscribe_fallbacks.begin(), uniscribe_fallbacks.end());
   }
 
   // Add Segoe UI and its associated linked fonts to the fallback font list to
   // ensure that the fallback list covers the basic cases.
   // http://crbug.com/467459. On some Windows configurations the default font
   // could be a raster font like System, which would not give us a reasonable
   // fallback font list.
-  std::vector<std::string> default_fallback_families =
-      GetFallbackFontFamilies("Segoe UI");
-  fallback_families.insert(fallback_families.end(),
-      default_fallback_families.begin(), default_fallback_families.end());
+  if (!LowerCaseEqualsASCII(primary_family, "segoe ui") &&
+      !LowerCaseEqualsASCII(uniscribe_family, "segoe ui")) {
+    std::vector<std::string> default_fallback_families =
+        GetFallbackFontFamilies("Segoe UI");
+    fallback_families.insert(fallback_families.end(),
+        default_fallback_families.begin(), default_fallback_families.end());
+  }
 #endif
 
   // Get rid of duplicate fonts in the fallback list. We use the std::unique
   // algorithm for this. However for this function to work we need to sort
   // the font list as the unique algorithm relies on duplicates being adjacent.
   // TODO(ananta)
   // Sorting the list changes the order in which fonts are evaluated. This may
   // cause problems in the way some characters appear. It may be best to do
   // font fallback on the same lines as blink or skia which do this based on
   // character glyph mapping.
@@ skipping 202 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