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

src/core/SkPixelRef.cpp

Index: src/core/SkPixelRef.cpp
diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index d7117617f62e4243c6b36935393df128b277b293..0825760ccd5e170a77ae56ef258b68f932c5781b 100644
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -307,13 +307,13 @@ void SkPixelRef::restoreMutability() {
     fMutability = kMutable;
 }
 
-bool SkPixelRef::readPixels(SkBitmap* dst, const SkIRect* subset) {
-    return this->onReadPixels(dst, subset);
+bool SkPixelRef::readPixels(SkBitmap* dst, SkColorType ct, const SkIRect* subset) {
+    return this->onReadPixels(dst, ct, subset);
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
-bool SkPixelRef::onReadPixels(SkBitmap* dst, const SkIRect* subset) {
+bool SkPixelRef::onReadPixels(SkBitmap* dst, SkColorType, const SkIRect* subset) {
     return false;
 }