code: public Observable<MetricsResult> getAsync(String appId, MetricId metricId) {
          return getWithServiceResponseAsync(appId, metricId).map(new Func1<ServiceResponse<MetricsResult>, MetricsResult>() {
              @Override
              public MetricsResult call(ServiceResponse<MetricsResult> response) {
                  return response.body();
              }
          });
      }
docs: Retrieve metric data.
  Gets metric values for a single metric.
  
  @param appId ID of the application. This is Application ID from the API Access settings blade in the Azure portal.
  @param metricId ID of the metric. This is either a standard AI metric, or an application-specific custom metric. Possible values include: 'requests/count', 'requests/duration', 'requests/failed', 'users/count', 'users/authenticated', 'pageViews/count', 'pageViews/duration', 'client/processingDuration', 'client/receiveDuration', 'client/networkDuration', 'client/sendDuration', 'client/totalDuration', 'dependencies/count', 'dependencies/failed', 'dependencies/duration', 'exceptions/count', 'exceptions/browser', 'exceptions/server', 'sessions/count', 'performanceCounters/requestExecutionTime', 'performanceCounters/requestsPerSecond', 'performanceCounters/requestsInQueue', 'performanceCounters/memoryAvailableBytes', 'performanceCounters/exceptionsPerSecond', 'performanceCounters/processCpuPercentage', 'performanceCounters/processIOBytesPerSecond', 'performanceCounters/processPrivateBytes', 'performanceCounters/processorCpuPercentage', 'availabilityResults/availabilityPercentage', 'availabilityResults/duration', 'billing/telemetryCount', 'customEvents/count'
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the MetricsResult object