Skip AnimatedGifEncoder for original GIFs.

Fixes #184.

library/src/androidTest/java/com/bumptech/glide/load/resource/gif/GifResourceEncoderTest.java

@@ -8,12 +8,14 @@ import com.bumptech.glide.gifencoder.AnimatedGifEncoder;
 import com.bumptech.glide.load.Transformation;
 import com.bumptech.glide.load.engine.Resource;
 import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
+import com.bumptech.glide.load.resource.UnitTransformation;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.InOrder;
 import org.robolectric.RobolectricTestRunner;
 
+import java.io.IOException;
 import java.io.OutputStream;
 
 import static org.junit.Assert.assertEquals;
@@ -24,6 +26,7 @@ import static org.mockito.Matchers.anyInt;
 import static org.mockito.Matchers.eq;
 import static org.mockito.Mockito.inOrder;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -236,6 +239,23 @@ public class GifResourceEncoderTest {
         order.verify(frameResource).recycle();
     }
 
+    @Test
+    public void testWritesBytesDirectlyToDiskIfTransformationIsUnitTransformation() throws IOException {
+        when(gifDrawable.getFrameTransformation()).thenReturn(UnitTransformation.<Bitmap>get());
+        byte[] expected = "expected".getBytes();
+        when(gifDrawable.getData()).thenReturn(expected);
+
+        OutputStream os = mock(OutputStream.class);
+
+        encoder.encode(resource, os);
+
+        verify(os).write(eq(expected));
+
+        verify(gifEncoder, never()).start(any(OutputStream.class));
+        verify(parser, never()).setData(any(byte[].class));
+        verify(parser, never()).parseHeader();
+    }
+
     @Test
     public void testHasValidId() {
         assertEquals("", encoder.getId());

library/src/main/java/com/bumptech/glide/load/resource/gif/GifResourceEncoder.java

@@ -10,9 +10,11 @@ import com.bumptech.glide.load.ResourceEncoder;
 import com.bumptech.glide.load.Transformation;
 import com.bumptech.glide.load.engine.Resource;
 import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
+import com.bumptech.glide.load.resource.UnitTransformation;
 import com.bumptech.glide.load.resource.bitmap.BitmapResource;
 import com.bumptech.glide.util.LogTime;
 
+import java.io.IOException;
 import java.io.OutputStream;
 
 /**
@@ -42,6 +44,11 @@ public class GifResourceEncoder implements ResourceEncoder<GifDrawable> {
         long startTime = LogTime.getLogTime();
 
         GifDrawable drawable = resource.get();
+        Transformation<Bitmap> transformation = drawable.getFrameTransformation();
+        if (transformation instanceof UnitTransformation) {
+            return writeDataDirect(drawable.getData(), os);
+        }
+
         GifDecoder decoder = decodeHeaders(drawable.getData());
 
         AnimatedGifEncoder encoder = factory.buildEncoder();
@@ -49,7 +56,6 @@ public class GifResourceEncoder implements ResourceEncoder<GifDrawable> {
             return false;
         }
 
-        Transformation<Bitmap> transformation = drawable.getFrameTransformation();
         for (int i = 0; i < decoder.getFrameCount(); i++) {
             Bitmap currentFrame = decoder.getNextFrame();
             Resource<Bitmap> transformedResource = getTransformedFrame(currentFrame, transformation, drawable);
@@ -77,6 +83,19 @@ public class GifResourceEncoder implements ResourceEncoder<GifDrawable> {
         return result;
     }
 
+    private boolean writeDataDirect(byte[] data, OutputStream os) {
+        boolean success = true;
+        try {
+            os.write(data);
+        } catch (IOException e) {
+            if (Log.isLoggable(TAG, Log.DEBUG)) {
+                Log.d(TAG, "Failed to write data to output stream in GifResourceEncoder", e);
+            }
+            success = false;
+        }
+        return success;
+    }
+
     private GifDecoder decodeHeaders(byte[] data) {
         GifHeaderParser parser = factory.buildParser();
         parser.setData(data);