Add a Bitmap -> GlideDrawable transcoder.

library/src/main/java/com/bumptech/glide/load/resource/transcode/BitmapToGlideDrawableTranscoder.java

+package com.bumptech.glide.load.resource.transcode;
+
+import android.content.Context;
+import android.graphics.Bitmap;
+import com.bumptech.glide.load.engine.Resource;
+import com.bumptech.glide.load.resource.drawable.GlideDrawable;
+
+/**
+ * A wrapper for {@link com.bumptech.glide.load.resource.transcode.GlideBitmapDrawableTranscoder} that transcodes
+ * to {@link com.bumptech.glide.load.resource.drawable.GlideDrawable} rather than
+ * {@link com.bumptech.glide.load.resource.bitmap.GlideBitmapDrawable}.
+ *
+ * TODO: use ? extends GlideDrawable rather than GlideDrawable directly and remove this class.
+ */
+public class BitmapToGlideDrawableTranscoder implements ResourceTranscoder<Bitmap, GlideDrawable> {
+
+    private final GlideBitmapDrawableTranscoder glideBitmapDrawableTranscoder;
+
+    public BitmapToGlideDrawableTranscoder(Context context) {
+        this(new GlideBitmapDrawableTranscoder(context));
+    }
+
+    public BitmapToGlideDrawableTranscoder(GlideBitmapDrawableTranscoder glideBitmapDrawableTranscoder) {
+        this.glideBitmapDrawableTranscoder = glideBitmapDrawableTranscoder;
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public Resource<GlideDrawable> transcode(Resource<Bitmap> toTranscode) {
+        return (Resource<GlideDrawable>) (Resource<? extends GlideDrawable>)
+                glideBitmapDrawableTranscoder.transcode(toTranscode);
+    }
+
+    @Override
+    public String getId() {
+        return glideBitmapDrawableTranscoder.getId();
+    }
+}

library/src/main/java/com/bumptech/glide/load/resource/transcode/GlideBitmapDrawableTranscoder.java

 package com.bumptech.glide.load.resource.transcode;
 
+import android.content.Context;
 import android.content.res.Resources;
 import android.graphics.Bitmap;
+import com.bumptech.glide.Glide;
 import com.bumptech.glide.load.engine.Resource;
 import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
 import com.bumptech.glide.load.resource.bitmap.GlideBitmapDrawable;
@@ -15,6 +17,10 @@ public class GlideBitmapDrawableTranscoder implements ResourceTranscoder<Bitmap,
     private final Resources resources;
     private final BitmapPool bitmapPool;
 
+    public GlideBitmapDrawableTranscoder(Context context) {
+        this(context.getResources(), Glide.get(context).getBitmapPool());
+    }
+
     public GlideBitmapDrawableTranscoder(Resources resources, BitmapPool bitmapPool) {
         this.resources = resources;
         this.bitmapPool = bitmapPool;