Make SkGpuDevice know its alpha type

src/gpu/GrSurface.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrSurface.h"
 #include "GrSurfacePriv.h"
 
@@ skipping 23 matching lines @@
         return false;
     }
     GrRenderTarget* target = this->asRenderTarget();
     if (target) {
         return context->readRenderTargetPixels(target, left, top, width, height, config, buffer,
                                                rowBytes, pixelOpsFlags);
     }
     return false;
 }
 
-SkImageInfo GrSurface::info() const {
+SkImageInfo GrSurface::info(SkAlphaType alphaType) const {
     SkColorType colorType;
     SkColorProfileType profileType;
     if (!GrPixelConfig2ColorAndProfileType(this->config(), &colorType, &profileType)) {
         sk_throw();
     }
-    return SkImageInfo::Make(this->width(), this->height(), colorType, kPremul_SkAlphaType,
+    return SkImageInfo::Make(this->width(), this->height(), colorType, alphaType,
                              profileType);
 }
 
 // TODO: This should probably be a non-member helper function. It might only be needed in
 // debug or developer builds.
 bool GrSurface::savePixels(const char* filename) {
     SkBitmap bm;
     if (!bm.tryAllocPixels(SkImageInfo::MakeN32Premul(this->width(), this->height()))) {
         return false;
     }
@@ skipping 67 matching lines @@
 
 void GrSurface::onRelease() {
     this->invokeReleaseProc();
     this->INHERITED::onRelease();
 }
 
 void GrSurface::onAbandon() {
     this->invokeReleaseProc();
     this->INHERITED::onAbandon();
 }