Allow the default generic font family settings to find the first available font

ui/gfx/font.cc

Index: ui/gfx/font.cc
diff --git a/ui/gfx/font.cc b/ui/gfx/font.cc
index ac7b7491a6cdcb98caa8e889900db693f454d9f6..b657cde7bb0253b4b024d0ecedb06940fcd33a02 100644
--- a/ui/gfx/font.cc
+++ b/ui/gfx/font.cc
@@ -4,8 +4,11 @@
 
 #include "ui/gfx/font.h"
 
+#include "base/strings/string_split.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
+#include "third_party/skia/include/core/SkTypeface.h"
+#include "third_party/skia/include/ports/SkFontMgr.h"
 #include "ui/gfx/platform_font.h"
 
 namespace gfx {
@@ -91,6 +94,30 @@ NativeFont Font::GetNativeFont() const {
 }
 #endif
 
+bool IsFontFamilyAvailable(const std::string& family, SkFontMgr* fontManager) {
+#if defined(OS_LINUX)
+  sk_sp<SkTypeface> typeface(
+      fontManager->legacyCreateTypeface(family.c_str(), SkFontStyle()));

[msw, 2016/10/26 20:33:49]

Why are we using a legacy skia codepath here and an unusual codepath below?
gfx::Font has a constructor that takes a name and size, then you could apply a
style as needed. Why would we want to construct fonts differently here than
elsewhere in ui/gfx and chrome?

[kojii, 2016/10/26 22:20:03]

Because if I create gfx::Font("that does not exist"), it fallbacks to
kFallbackFontFamilyName, and it doesn't tell if the specified name exists or
not.

[msw, 2016/10/27 00:04:18]

Since FontList::ParseDescription requires a size, would SkTypeface::MakeFromName
help? The less repetition of deprecated lower-level skia code we have in chrome,
the better. (that said, it's good this follows a pattern similar to that in
SkTypeface::MakeFromName, perhaps mention that in a comment?).

Perhaps gfx::Font could have a flag indicating if it fell back to some default,
but I'm not entirely sure we need do that just yet.

+  return typeface;
+#else
+  sk_sp<SkFontStyleSet> sset(fontManager->matchFamily(family.c_str()));

[msw, 2016/10/26 20:33:49]

nit: |style_set| or just |set|

[kojii, 2016/10/26 22:20:03]

Done.

+  return sset && sset->count();
+#endif
+}
+
+std::string Font::FirstAvailableOrFirst(const std::string& font_name_list) {
+  std::vector<std::string> families = base::SplitString(

[msw, 2016/10/26 20:33:49]

Could we use gfx::FontList's constructor that takes a font description string
here? Perhaps the callers could just do something like gfx::Font
first(gfx::FontList(description_string).DeriveFoo(foo).GetPrimaryFont());

[kojii, 2016/10/26 22:20:03]

Hmm...FontList::ParseDescription() needs size, and include empty entries.

If this looks like not generic enough to put in gfx, I can move to
font_settings_utils and make a copy in Blink. Does that work better? I actually
did so initially but looked for somewhere to share the code in PS10. But the
code is small and probably not too generic, I'm fine not to share if doing so
looks better.

PS13 shows the un-shared version.

[msw, 2016/10/27 00:04:18]

Hmm, perhaps derat or asvitkine would have a better idea if this code belongs in
gfx... or perhaps there's some better location for sharing blink font util code
between c/b/ui/webui/options and third_party/WebKit/Source/platform/fonts/...

+      font_name_list, ",", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
+  if (families.empty())
+    return std::string();
+  sk_sp<SkFontMgr> fm(SkFontMgr::RefDefault());
+  for (auto& family : families) {
+    if (IsFontFamilyAvailable(family, fm.get()))
+      return family;
+  }
+  return families[0];
+}
+
 #ifndef NDEBUG
 std::ostream& operator<<(std::ostream& stream, const Font::Weight weight) {
   return stream << static_cast<int>(weight);