Add FontCache API for retrieving prioritized fallback fonts

third_party/WebKit/Source/platform/fonts/FontCache.cpp

Index: third_party/WebKit/Source/platform/fonts/FontCache.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/FontCache.cpp b/third_party/WebKit/Source/platform/fonts/FontCache.cpp
index 462f0d04ff0cd9443d31061f85b23e7733a538f1..a9cf27c8c50d1e2b94553347070e567db26bea86 100644
--- a/third_party/WebKit/Source/platform/fonts/FontCache.cpp
+++ b/third_party/WebKit/Source/platform/fonts/FontCache.cpp
@@ -194,6 +194,41 @@ SimpleFontData* FontCache::getNonRetainedLastResortFallbackFont(const FontDescri
     return getLastResortFallbackFont(fontDescription, DoNotRetain).leakRef();
 }
 
+template <FontFallbackPriority fallbackPriority>
+const Vector<AtomicString>* FontCache::initAndGetFontListForFallbackPriority(const FontDescription& fontDescription)
+{
+    DEFINE_STATIC_LOCAL(Vector<AtomicString>, fontsList, ());
+    DEFINE_STATIC_LOCAL(bool, fontsListInitialized, (false));
+    if (fontsListInitialized)
+        return &fontsList;
+
+    for (auto fontCandidate :
+        platformFontListForFallbackPriority(fallbackPriority)) {
+        if (isPlatformFontAvailable(fontDescription, fontCandidate))
+            fontsList.append(fontCandidate);
+    }
+    fontsListInitialized = true;
+    return &fontsList;
+}
+
+const Vector<AtomicString>* FontCache::fontListForFallbackPriority(const FontDescription& fontDescription, FontFallbackPriority fallbackPriority)
+{
+    // Explicit template instantiations for valid values.
+    switch (fallbackPriority) {
+    case FontFallbackPriority::Symbols:
+        return initAndGetFontListForFallbackPriority<FontFallbackPriority::Symbols>(fontDescription);
+    case FontFallbackPriority::Math:
+        return initAndGetFontListForFallbackPriority<FontFallbackPriority::Math>(fontDescription);
+    case FontFallbackPriority::EmojiText:
+        return initAndGetFontListForFallbackPriority<FontFallbackPriority::EmojiText>(fontDescription);
+    case FontFallbackPriority::EmojiEmoji:
+        return initAndGetFontListForFallbackPriority<FontFallbackPriority::EmojiEmoji>(fontDescription);
+    default:
+        ASSERT_NOT_REACHED();
+        return nullptr;
+    }
+}
+
 void FontCache::releaseFontData(const SimpleFontData* fontData)
 {
     ASSERT(gFontDataCache);