Fix png encoding in skia debugger

tools/skiaserve/Request.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Request.h"
 
 #include "SkPictureRecorder.h"
@@ skipping 41 matching lines @@
 
 SkData* Request::writeCanvasToPng(SkCanvas* canvas) {
     // capture pixels
     SkAutoTDelete<SkBitmap> bmp(this->getBitmapFromCanvas(canvas));
     SkASSERT(bmp);
 
     // Convert to format suitable for PNG output
     sk_sp<SkData> encodedBitmap = sk_tools::encode_bitmap_for_png(*bmp);
     SkASSERT(encodedBitmap.get());
 
-    // write to png
+    // write to an opaque png (black background)
     SkDynamicMemoryWStream buffer;
-    SkDrawCommand::WritePNG((const png_bytep) encodedBitmap->writable_data(),
-                            bmp->width(), bmp->height(),
-                            buffer);
+    SkDrawCommand::WritePNG((const png_bytep) encodedBitmap->bytes(), bmp->width(), bmp->height(),
+                            buffer, true);
     return buffer.copyToData();
 }
 
 SkCanvas* Request::getCanvas() {
 #if SK_SUPPORT_GPU
     GrContextFactory* factory = fContextFactory;
     GLTestContext* gl = factory->getContextInfo(GrContextFactory::kNativeGL_ContextType,
                                                 GrContextFactory::kNone_ContextOptions).glContext();
     if (!gl) {
         gl = factory->getContextInfo(GrContextFactory::kMESA_ContextType,
@@ skipping 222 matching lines @@
     SkASSERT(bitmap);
 
     // Convert to format suitable for inspection
     sk_sp<SkData> encodedBitmap = sk_tools::encode_bitmap_for_png(*bitmap);
     SkASSERT(encodedBitmap.get());
 
     const uint8_t* start = encodedBitmap->bytes() + ((y * bitmap->width() + x) * 4);
     SkColor result = SkColorSetARGB(start[3], start[0], start[1], start[2]);
     return result;
 }