Implement function entry breakpoints in Observatory debugger.

runtime/vm/service/service.idl

 //
 // TODO(turnidge): Finish writing an idl description of the service protocol.
 //
 
 interface Service {
   getVM() VM
 
   getFlagList() FlagList
 
   setFlag(name string, value string) Response
 
   getObject(isolateId string, objectId string) Object
 
   // The response is a subtype of Object or ObjectRef.
   getObjectByAddress(address string, ref bool) Response
 
   // Returns the list of breakpoints for an isolate.
   getBreakpoints(isolateId string) BreakpointList
 
   // Adds a breakpoint at the specified line.
   //
   // TODO(turnidge): Make line an int instead of a string.
   addBreakpoint(isolateId string,
                 scriptId string,
                 line string) Breakpoint
 
+  // Adds a breakpoint at the entrypoint of the specified function.
+  addBreakpointAtEntry(isolateId string,
+                       functionId string) Breakpoint
+
   // Removes the specified breakpoint
   removeBreakpoint(isolateId string, breakpointId string) Response
 
   // Requests that an isolate pause execution.
   pause(isolateId string) Response
 
   // Requests that an isolate resume execution.
   //
   // <code>step</code> is optional and indicates whether execution
   // should single-step.
@@ skipping 395 matching lines @@
   VMOnly
   None
 }
 
 // A <code>MetricSelector</code> is used to indicate which list of metrics
 // should be retrieved from an isolate.
 enum MetricSelector {
   Dart,
   Native,
 }