LibDraw: Introduce an Emoji class

This class can locate and load emojis, which are expected to be stored
as regular PNG images at /res/emoji/U+XXXX.png, where XXXX is the
character codepoint.

https://github.com/SerenityOS/serenity/issues/490

Libraries/LibDraw/Emoji.cpp

@@ -0,0 +1,27 @@
+#include "Emoji.h"
+#include "GraphicsBitmap.h"
+#include <AK/AKString.h>
+#include <AK/HashMap.h>
+
+static HashMap<u32, Emoji> s_emojis;
+
+Emoji::Emoji(NonnullRefPtr<GraphicsBitmap> bitmap)
+    : m_bitmap(move(bitmap))
+{
+}
+
+const Emoji* Emoji::emoji_for_codepoint(u32 codepoint)
+{
+    auto it = s_emojis.find(codepoint);
+    if (it != s_emojis.end())
+        return &(*it).value;
+
+    String path = String::format("/res/emoji/U+%X.png", codepoint);
+
+    auto bitmap = GraphicsBitmap::load_from_file(path);
+    if (!bitmap)
+        return nullptr;
+
+    s_emojis.set(codepoint, Emoji { bitmap.release_nonnull() });
+    return &(*s_emojis.find(codepoint)).value;
+}

Libraries/LibDraw/Emoji.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <AK/Types.h>
+#include <AK/NonnullRefPtr.h>
+
+class GraphicsBitmap;
+
+class Emoji {
+ public:
+    ~Emoji() {}
+
+    static const Emoji* emoji_for_codepoint(u32 codepoint);
+    const GraphicsBitmap& bitmap() const { return m_bitmap; }
+
+private:
+    explicit Emoji(NonnullRefPtr<GraphicsBitmap>);
+
+    NonnullRefPtr<GraphicsBitmap> m_bitmap;
+};

Libraries/LibDraw/Makefile

@@ -9,7 +9,8 @@ OBJS = \
     Painter.o \
     PNGLoader.o \
     Rect.o \
-    StylePainter.o
+    StylePainter.o \
+    Emoji.o
 
 LIBRARY = libdraw.a
 DEFINES += -DUSERLAND