Add a SymbolsIterator to aid with Symbols Segmentation

third_party/WebKit/Source/platform/fonts/FontFallbackPriority.h

+// Copyright 2015 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.
+
+#ifndef FontFallbackPriority_h
+#define FontFallbackPriority_h
+
+namespace blink {
+
+enum class FontFallbackPriority {
+    // For regular non-symbols text,
+    // normal text fallback in FontFallbackIterator
+    Text,
+    // For non-emoji symbols
+    Symbols,
+    // For math & technical symbols
+    Math,
+    // For Emoji text presentation,
+    // compare http://unicode.org/Public/emoji/2.0/emoji-data.txt
+    EmojiText,
+    // For Emoji presentation
+    EmojiEmoji,

[wkorman, 2016/01/22 00:50:45]

EmojiImage / EmojiIcon is more what I would expect to see for this one but I may
just not be familiar with nomenclature used in emoji related code. Reading
'EmojiEmoji' everywhere looks a bit like a typo to a naive reader.

If we keep it the way it is maybe add a comment explaining?

+    Invalid
+};
+
+bool isNonTextFallbackPriority(FontFallbackPriority);
+
+}; // namespace blink
+
+#endif