Make SkBitmap::CopyTo respect requested dst color type when bitmap is texture backed.

src/core/SkBitmapDevice.cpp

Index: src/core/SkBitmapDevice.cpp
diff --git a/src/core/SkBitmapDevice.cpp b/src/core/SkBitmapDevice.cpp
index ac3b9df0827ed51aedfb5f5520c7457ced5e7a8a..749e91de75e1770f5d921fde2ef0653850bdb7ec 100644
--- a/src/core/SkBitmapDevice.cpp
+++ b/src/core/SkBitmapDevice.cpp
@@ -286,7 +286,7 @@ void SkBitmapDevice::drawBitmapRect(const SkDraw& draw, const SkBitmap& bitmap,
         if(bitmap.pixelRef()->getTexture()) {
             // Accelerated source canvas, don't use extractSubset but readPixels to get the subset.
             // This way, the pixels are copied in CPU memory instead of GPU memory.
-            bitmap.pixelRef()->readPixels(&tmpBitmap, &srcIR);
+            bitmap.pixelRef()->readPixels(&tmpBitmap, kN32_SkColorType, &srcIR);
         } else {
             if (!bitmap.extractSubset(&tmpBitmap, srcIR)) {
                 return;