Summary: This diff implements ImageLoadEvents (ON_LOAD, ON_LOAD_END and ON_LOAD_START) in RCTImageView. ON_ERROR and ON_PROGRESS are easy to implement, too, but these 2 are supposed to carry extra information (error message and progress) but ImageLoadEvent doesn't support a payload yet (I'll add them in a separate patch).
Reviewed By: ahmedre
Differential Revision: D2824772
Summary: Minor cleanup; renames BitmapRequestHelper to PipelineRequestHelper and adds BitmapUpdateListener interface. I plan reusing these classes in an upcoming RCTTextInlineImage implementation.
Reviewed By: ahmedre
Differential Revision: D2792535