Add FontCache API for retrieving prioritized fallback fonts

third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp

Index: third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp b/third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp
index 591ba4f2cbf8872ef6eac5ec127e8ec2ee268ed0..7fa21205653ba5f7b2e788eb81bed1331ac889f8 100644
--- a/third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp
+++ b/third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp
@@ -43,6 +43,35 @@
 #include "wtf/text/CString.h"
 #include <unicode/locid.h>
 
+// Unfortunately, these chosen font names require a bit of experimentation and
+// researching on the respective platforms as to what works best and is widely
+// available. They may require further manual tuning. Mozilla's choices in the
+// gfxPlatform*::GetCommonFallbackFonts methods collects some of the outcome of
+// this experimentation. On Android, the available fonts in
+// /system/etc/fonts.xml give a clearer picture of which fonts are available and
+// can be widely used successfully. On Linux, updating and improving this list
+// requires finding out widely used distribution fonts, for example on current
+// Ubuntu versions.
+#if OS(WIN)
+const char* kColorEmojiFonts[] = { "Segoe UI Emoji" };
+const char* kTextEmojiFonts[] = { "Segoe UI Symbol" };
+const char* kSymbolsFonts[] = { "Segoe UI Symbol" };
+const char* kMathFonts[] = { "Cambria Math", "Segoe UI Symbol", "Code2000" };
+#elif OS(ANDROID)
+// Due to crbug.com/322658 we cannot properly specify Android font family names here,
+// The way Skia's SkFontMgr_android gives them canonical names, we can however
+// reference the Noto Color Emoji font under "56##fallback" on Android 6.0.1
+const char* kColorEmojiFonts[] = { "56##fallback", "Noto Color Emoji", "Android Emoji" };
+const char* kTextEmojiFonts[] = { "Droid Sans Fallback" };
+const char* kSymbolsFonts[] = { "Droid Sans Fallback" };
+const char* kMathFonts[] = { "Droid Sans Fallback" };
+#elif OS(LINUX)
+const char* kColorEmojiFonts[] = { "Noto Color Emoji", "Noto Sans Symbols", "Symbola" };
+const char* kTextEmojiFonts[] = { "Noto Sans Symbols", "Symbola" };
+const char* kSymbolsFonts[] = { "FreeSerif", "FreeMono" };
+const char* kMathFonts[] = { "FreeSerif", "FreeMono" };
+#endif
+
 #if !OS(WIN) && !OS(ANDROID)
 #include "SkFontConfigInterface.h"
 
@@ -161,6 +190,33 @@ PassRefPtr<SimpleFontData> FontCache::getLastResortFallbackFont(const FontDescri
     return fontDataFromFontPlatformData(fontPlatformData, shouldRetain);
 }
 
+

[wkorman, 2016/02/02 19:04:08]

-1 blank

+const Vector<AtomicString> FontCache::platformFontListForFallbackPriority(FontFallbackPriority fallbackPriority) const
+{
+    Vector<AtomicString> returnVector;
+    switch (fallbackPriority) {
+    case FontFallbackPriority::EmojiEmoji:
+        for (size_t i = 0; i < WTF_ARRAY_LENGTH(kColorEmojiFonts); ++i)

[wkorman, 2016/02/02 19:04:08]

Could just set local var to the right array for each case and then do the for
loop once below switch on that.

[drott, 2016/02/02 22:27:01]

I've tried doing that but an array cannot be assigned to a local array, only a
pointer, and then I lose the ability to figure out the WTF_ARRAY_LENGTH, so I
would have to store the length as well. I don't think it would become much
prettier in that case.

+            returnVector.append(kColorEmojiFonts[i]);
+        break;
+    case FontFallbackPriority::EmojiText:
+        for (size_t i = 0; i < WTF_ARRAY_LENGTH(kTextEmojiFonts); ++i)
+            returnVector.append(kTextEmojiFonts[i]);
+        break;
+    case FontFallbackPriority::Math:
+        for (size_t i = 0; i < WTF_ARRAY_LENGTH(kMathFonts); ++i)
+            returnVector.append(kMathFonts[i]);
+        break;
+    case FontFallbackPriority::Symbols:
+        for (size_t i = 0; i < WTF_ARRAY_LENGTH(kSymbolsFonts); ++i)
+            returnVector.append(kSymbolsFonts[i]);
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+    }
+    return returnVector;
+}
+
 #if OS(WIN)
 static inline SkFontStyle fontStyle(const FontDescription& fontDescription)
 {