Add onImageInfo call to SkImage_Base.

src/image/SkImage_Base.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_Base_DEFINED
 #define SkImage_Base_DEFINED
 
 #include "SkAtomics.h"
 #include "SkImage.h"
 #include "SkSurface.h"
 
 #include <new>
 
 class GrTextureParams;
 class SkImageCacherator;
 
 enum {
     kNeedNewImageUniqueID = 0
 };
 
 class SkImage_Base : public SkImage {
 public:
     SkImage_Base(int width, int height, uint32_t uniqueID);
     virtual ~SkImage_Base();
 
+    // User: returns image info for this SkImage.
+    // Implementors: if you can not return the value, return an invalid ImageInfo with w=0 & h=0
+    // & unknown color space.
+    virtual SkImageInfo onImageInfo() const = 0;
+
     virtual bool onPeekPixels(SkPixmap*) const { return false; }
 
     // Default impl calls onDraw
     virtual bool onReadPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRowBytes,
                               int srcX, int srcY, CachingHint) const;
 
     virtual GrTexture* peekTexture() const { return nullptr; }
     virtual SkImageCacherator* peekCacherator() const { return nullptr; }
 
     // return a read-only copy of the pixels. We promise to not modify them,
@@ skipping 41 matching lines @@
 
 static inline SkImage_Base* as_IB(const sk_sp<SkImage>& image) {
     return static_cast<SkImage_Base*>(image.get());
 }
 
 static inline const SkImage_Base* as_IB(const SkImage* image) {
     return static_cast<const SkImage_Base*>(image);
 }
 
 #endif