Retain bounds when mutating GlideBitmapDrawable.

Follows the same pattern as BitmapDrawable in the
Android framework.

Fixes #118

library/src/androidTest/java/com/bumptech/glide/load/resource/bitmap/GlideBitmapDrawableTest.java

 package com.bumptech.glide.load.resource.bitmap;
 
 import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.ColorFilter;
+import android.graphics.LightingColorFilter;
+import android.graphics.Paint;
 import android.graphics.PixelFormat;
+import android.graphics.Rect;
 import android.graphics.drawable.Drawable;
-
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
 import org.robolectric.Robolectric;
 import org.robolectric.RobolectricTestRunner;
 
+import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertThat;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Matchers.isNull;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 
 @RunWith(RobolectricTestRunner.class)
 public class GlideBitmapDrawableTest {
@@ -80,11 +93,6 @@ public class GlideBitmapDrawableTest {
         assertEquals(drawable.getBitmap(), newDrawable.getBitmap());
     }
 
-    @Test
-    public void testMutateReturnsNewDrawable() {
-        assertNotSame(drawable, drawable.mutate());
-    }
-
     @Test
     public void testMutatedDrawableIsGlideBitmapDrawable() {
         Drawable newDrawable = drawable.mutate();
@@ -96,4 +104,61 @@ public class GlideBitmapDrawableTest {
         GlideBitmapDrawable mutated = (GlideBitmapDrawable) drawable.mutate();
         assertEquals(drawable.getBitmap(), mutated.getBitmap());
     }
+
+    @Test
+    public void testRetainsSameBoundsAcrossMutation() {
+        Rect bounds = new Rect(0, 0, 100, 100);
+        drawable.setBounds(bounds);
+        drawable.onBoundsChange(bounds);
+        Canvas canvas = mock(Canvas.class);
+        drawable.draw(canvas);
+
+        Drawable mutated = drawable.mutate();
+        mutated.draw(canvas);
+
+        assertThat(mutated.getBounds(), equalTo(bounds));
+        verify(canvas, times(2)).drawBitmap(eq(bitmap), isNull(Rect.class), eq(bounds), any(Paint.class));
+    }
+
+    @Test
+    public void testMutatedDrawableUsesNewPaint() {
+        drawable.setAlpha(1);
+        Drawable newDrawable = drawable.getConstantState().newDrawable();
+        Drawable mutated = drawable.mutate();
+        mutated.setAlpha(100);
+
+        Canvas canvas = mock(Canvas.class);
+        doAnswer(new Answer() {
+            @Override
+            public Object answer(InvocationOnMock invocation) throws Throwable {
+                Paint paint = (Paint) invocation.getArguments()[3];
+                assertThat(paint.getAlpha(), equalTo(1));
+                return null;
+            }
+        }).when(canvas).drawBitmap(any(Bitmap.class), any(Rect.class), any(Rect.class), any(Paint.class));
+        newDrawable.draw(canvas);
+        verify(canvas).drawBitmap(eq(bitmap), any(Rect.class), any(Rect.class), any(Paint.class));
+    }
+
+    @Test
+    public void testMutatedDrawableUsesNewColorFilter() {
+        final ColorFilter originalColorFilter = new LightingColorFilter(1, 1);
+        drawable.setColorFilter(originalColorFilter);
+        Drawable newDrawable = drawable.getConstantState().newDrawable();
+        Drawable mutated = drawable.mutate();
+        ColorFilter newColorFilter = new LightingColorFilter(2, 2);
+        mutated.setColorFilter(newColorFilter);
+
+        Canvas canvas = mock(Canvas.class);
+        doAnswer(new Answer() {
+            @Override
+            public Object answer(InvocationOnMock invocation) throws Throwable {
+                Paint paint = (Paint) invocation.getArguments()[3];
+                assertThat(paint.getColorFilter(), equalTo(originalColorFilter));
+                return null;
+            }
+        }).when(canvas).drawBitmap(any(Bitmap.class), any(Rect.class), any(Rect.class), any(Paint.class));
+        newDrawable.draw(canvas);
+        verify(canvas).drawBitmap(eq(bitmap), any(Rect.class), any(Rect.class), any(Paint.class));
+    }
 }
\ No newline at end of file

library/src/main/java/com/bumptech/glide/load/resource/bitmap/GlideBitmapDrawable.java

@@ -21,6 +21,7 @@ public class GlideBitmapDrawable extends GlideDrawable {
     private int width;
     private int height;
     private boolean applyGravity;
+    private boolean mutated;
     private BitmapState state;
 
     public GlideBitmapDrawable(Resources res, Bitmap bitmap) {
@@ -120,7 +121,11 @@ public class GlideBitmapDrawable extends GlideDrawable {
 
     @Override
     public Drawable mutate() {
-        return new GlideBitmapDrawable(null, new BitmapState(state));
+        if (!mutated && super.mutate() == this) {
+            state = new BitmapState(state);
+            mutated = true;
+        }
+        return this;
     }
 
     public Bitmap getBitmap() {