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 1b9130ac759b25af82f568ca09d49b4ebce06e27..a7ca7b718171c73434e43233dae0d5ab7d75d4cc 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;