enable analysis server cmdline instrumentation log file option

pkg/analysis_server/lib/src/server/driver.dart

Index: pkg/analysis_server/lib/src/server/driver.dart
diff --git a/pkg/analysis_server/lib/src/server/driver.dart b/pkg/analysis_server/lib/src/server/driver.dart
index 1862b9ff4fbc677d5e08108d1797bbe27760917c..1f5bd4b10b8a0b53f7fe05a217af65f0d0ff1501 100644
--- a/pkg/analysis_server/lib/src/server/driver.dart
+++ b/pkg/analysis_server/lib/src/server/driver.dart
@@ -381,12 +381,14 @@ class Driver implements ServerStarter {
     //
     // Initialize the instrumentation service.
     //
-    if (instrumentationServer != null) {
-      String filePath = results[INSTRUMENTATION_LOG_FILE];
-      if (filePath != null) {
-        instrumentationServer = new MulticastInstrumentationServer(
-            [instrumentationServer, new FileInstrumentationServer(filePath)]);
-      }
+    String logFilePath = results[INSTRUMENTATION_LOG_FILE];
+    if (logFilePath != null) {
+      FileInstrumentationServer fileBasedServer =
+          new FileInstrumentationServer(logFilePath);
+      instrumentationServer = instrumentationServer != null
+          ? new MulticastInstrumentationServer(
+              [instrumentationServer, fileBasedServer])
+          : fileBasedServer;
     }
     InstrumentationService service =
         new InstrumentationService(instrumentationServer);