Add onImageInfo call to SkImage_Base.

src/image/SkImage_Base.h

Index: src/image/SkImage_Base.h
diff --git a/src/image/SkImage_Base.h b/src/image/SkImage_Base.h
index ec5556a50d3f3cda7d6190077374d74fcff96315..947af0e0d178629c8d1e7ce4a138ea305824ec3f 100644
--- a/src/image/SkImage_Base.h
+++ b/src/image/SkImage_Base.h
@@ -26,6 +26,11 @@ 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