remove unused parameter in onNewimageSnapshot

BUG=skia:

Change-Id: I59b4cbace841489698fb22828c35b82a738d06b3
Reviewed-on: https://skia-review.googlesource.com/6494
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/src/image/SkSurface_Raster.cpp b/src/image/SkSurface_Raster.cpp
index 2f26e7f..47e0dbe 100644
--- a/src/image/SkSurface_Raster.cpp
+++ b/src/image/SkSurface_Raster.cpp
@@ -24,7 +24,7 @@
 
     SkCanvas* onNewCanvas() override;
     sk_sp<SkSurface> onNewSurface(const SkImageInfo&) override;
-    sk_sp<SkImage> onNewImageSnapshot(SkBudgeted, SkCopyPixelsMode) override;
+    sk_sp<SkImage> onNewImageSnapshot(SkBudgeted) override;
     void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*) override;
     void onCopyOnWrite(ContentChangeMode) override;
     void onRestoreBackingMutability() override;
@@ -130,7 +130,8 @@
     canvas->drawBitmap(fBitmap, x, y, paint);
 }
 
-sk_sp<SkImage> SkSurface_Raster::onNewImageSnapshot(SkBudgeted, SkCopyPixelsMode cpm) {
+sk_sp<SkImage> SkSurface_Raster::onNewImageSnapshot(SkBudgeted) {
+    SkCopyPixelsMode cpm = kIfMutable_SkCopyPixelsMode;
     if (fWeOwnThePixels) {
         // SkImage_raster requires these pixels are immutable for its full lifetime.
         // We'll undo this via onRestoreBackingMutability() if we can avoid the COW.