Add onImageInfo call to SkImage_Base.

src/image/SkImage_Generator.cpp

Index: src/image/SkImage_Generator.cpp
diff --git a/src/image/SkImage_Generator.cpp b/src/image/SkImage_Generator.cpp
index 44dd7b11f83b8dfaff8d37a35a2e48c0d1201a09..b117322aa69f1d65ba0b0693344867cdc6bdb176 100644
--- a/src/image/SkImage_Generator.cpp
+++ b/src/image/SkImage_Generator.cpp
@@ -21,6 +21,10 @@ public:
         , fCache(cache) // take ownership
     {}
 
+    virtual SkImageInfo onImageInfo() const override {
+        return fCache->info();
+    }
+
     bool onReadPixels(const SkImageInfo&, void*, size_t, int srcX, int srcY, CachingHint) const override;
     SkImageCacherator* peekCacherator() const override { return fCache; }
     SkData* onRefEncoded(GrContext*) const override;