RenderTextHarfBuzz: Implement font fallback for Win and Linux

ui/gfx/font_fallback_linux.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/font_fallback.h"
+
+#include <fontconfig/fontconfig.h>
+
+namespace gfx {
+
+std::vector<std::string> GetFallbackFontFamilies(std::string font_family) {
+  std::vector<std::string> fallback_fonts;
+  FcPattern* pattern = FcPatternCreate();
+  FcValue family;
+  family.type = FcTypeString;
+  family.u.s = reinterpret_cast<const unsigned char*>(font_family.c_str());

[msw, 2014/06/30 17:35:53]

Maybe use FcChar8* to match the FC types like platform_font_pango.cc?

[ckocagil, 2014/07/04 15:30:15]

Done.

+  FcPatternAdd(pattern, FC_FAMILY, family, FcFalse);
+
+  FcConfigSubstitute(NULL, pattern, FcMatchPattern);

[msw, 2014/06/30 17:35:53]

Check the return value here? (I guess font_render_params_linux.cc doesn't)

[ckocagil, 2014/07/04 15:30:15]

Let's do it here anyway, done.

+  FcDefaultSubstitute(pattern);
+  FcResult result;
+  FcFontSet* fonts = FcFontSort(NULL, pattern, FcTrue, NULL, &result);
+
+  if (fonts) {
+    for (int i = 0; i < fonts->nfont; ++i) {
+      char* name = NULL;
+      FcPatternGetString(fonts->fonts[i], FC_FAMILY, 0,
+          reinterpret_cast<unsigned char**>(&name));
+      if (fallback_fonts.empty() || fallback_fonts.back() != name)

[msw, 2014/06/30 17:35:53]

Do we expect there to be adjacent duplicate entries?

[ckocagil, 2014/07/04 15:30:15]

Yes. Currently we only take the family name into account without looking at the
bold/italic/etc fields. There are can be than one font entry in the list with
the same family name and with varying bold/italic fields.

[msw, 2014/07/07 22:52:45]

That seems worth explaining in a short comment here.

[ckocagil, 2014/07/12 11:47:54]

Done.

+        fallback_fonts.push_back(std::string(name));
+    }
+
+    FcFontSetDestroy(fonts);
+  }
+
+  FcPatternDestroy(pattern);
+
+  if (fallback_fonts.empty())
+    fallback_fonts.push_back(font_family);
+
+  return fallback_fonts;
+}
+
+}  // namespace gfx