addBreakpointAtEntry abstract method
addBreakpointAtEntry RPC is used to add a breakpoint at the
entrypoint of some function.
If no breakpoint is possible at the function entry, the
102 (Cannot add
breakpoint) RPC error code is returned.
isolateId refers to an isolate which has exited, then the
Sentinel is returned.
Note that breakpoints are added and removed on a per-isolate basis.
Future<Breakpoint> addBreakpointAtEntry(String isolateId, String functionId);