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 {
+
+// http://unicode.org/reports/tr51/#Presentation_Style discusses the differences
+// between emoji in text and the emoji in emoji presentation. In that sense, the
+// EmojiEmoji wording is taken from there.  Also compare
+// http://unicode.org/Public/emoji/1.0/emoji-data.txt
+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 in text presentaiton
+    EmojiText,
+    // For emoji in emoji presentation
+    EmojiEmoji,
+    Invalid
+};
+
+bool isNonTextFallbackPriority(FontFallbackPriority);
+
+}; // namespace blink
+
+#endif