Use CTFontCreateForString for RenderTextHarfbuzz on Mac

ui/gfx/font_fallback_mac.mm

Index: ui/gfx/font_fallback_mac.mm
diff --git a/ui/gfx/font_fallback_mac.mm b/ui/gfx/font_fallback_mac.mm
index 6ad582dcc8edb42bf4307373ff6c44fb8545af35..6cfc7e36b8b713de6d9cfacfd347fcc0279bd98e 100644
--- a/ui/gfx/font_fallback_mac.mm
+++ b/ui/gfx/font_fallback_mac.mm
@@ -4,32 +4,45 @@
 
 #include "ui/gfx/font_fallback.h"
 
-#include <dlfcn.h>
+#include <CoreText/CoreText.h>
 #import <Foundation/Foundation.h>
-#include <string>
-#include <vector>
 
 #include "base/mac/foundation_util.h"
 #import "base/mac/mac_util.h"
+#include "base/mac/scoped_cftyperef.h"
 #import "base/strings/sys_string_conversions.h"
 #include "ui/gfx/font.h"
 
-// TODO(thakis): Remove this prototype once the deployment target is 10.8+.
-extern "C" CFArrayRef CTFontCopyDefaultCascadeListForLanguages(
-    CTFontRef font,
-    CFArrayRef languagePrefList);
-
 namespace gfx {
+namespace {
+
+// CTFontCreateForString() sometimes re-wraps its result in a new CTFontRef with
+// identical attributes. This wastes time shaping the text run and confounds
+// Skia's internal typeface cache.
+bool FontsEqual(CTFontRef lhs, CTFontRef rhs) {
+  if (lhs == rhs)
+    return true;
+
+  // Compare ATSFontRef typeface IDs. These are typedef uint32_t. Typically if
+  // RenderText decided to hunt for a fallback in the first place, this check
+  // fails and FontsEqual returns here.
+  if (CTFontGetPlatformFont(lhs, nil) != CTFontGetPlatformFont(rhs, nil))
+    return false;
+
+  // Comparing addresses of descriptors seems to be sufficient for other cases.
+  base::ScopedCFTypeRef<CTFontDescriptorRef> lhs_descriptor(
+      CTFontCopyFontDescriptor(lhs));
+  base::ScopedCFTypeRef<CTFontDescriptorRef> rhs_descriptor(
+      CTFontCopyFontDescriptor(rhs));
+  return lhs_descriptor.get() == rhs_descriptor.get();
+}
+
+}  // namespace
 
 std::vector<Font> GetFallbackFonts(const Font& font) {
   // On Mac "There is a system default cascade list (which is polymorphic, based
   // on the user's language setting and current font)" - CoreText Programming
   // Guide.
-  // The CoreText APIs provide CTFontCreateForString(font, string, range), but
-  // it requires a text string "hint", and the returned font can't be
-  // represented by name for easy retrieval later.
-  // In 10.8, CTFontCopyDefaultCascadeListForLanguages(font, language_list)
-  // showed up which is a good fit GetFallbackFonts().
   NSArray* languages = [[NSUserDefaults standardUserDefaults]
       stringArrayForKey:@"AppleLanguages"];
   CFArrayRef languages_cf = base::mac::NSToCFCast(languages);
@@ -56,4 +69,21 @@ std::vector<Font> GetFallbackFonts(const Font& font) {
   return fallback_fonts;
 }
 
+bool GetFallbackFont(const Font& font,
+                     const base::char16* text,
+                     int text_length,
+                     Font* result) {
+  base::ScopedCFTypeRef<CFStringRef> cf_string(
+      CFStringCreateWithCharactersNoCopy(kCFAllocatorDefault, text, text_length,
+                                         kCFAllocatorNull));
+  CTFontRef ct_font = base::mac::NSToCFCast(font.GetNativeFont());
+  base::ScopedCFTypeRef<CTFontRef> ct_result(
+      CTFontCreateForString(ct_font, cf_string, {0, text_length}));
+  if (FontsEqual(ct_font, ct_result))
+    return false;
+
+  *result = Font(base::mac::CFToNSCast(ct_result.get()));
+  return true;
+}
+
 }  // namespace gfx