code: public @CheckForNull
      SourceLineRange getMethodLine(String className, String methodName, String methodSignature) {
          return methodLineMap.get(new MethodDescriptor(className, methodName, methodSignature));
      }
docs: Look up the line number range for a method.
  
  @param className
  name of class containing the method
  @param methodName
  name of method
  @param methodSignature
  signature of method
  @return the line number range, or null if no line number is known for the
  method