Do not check for an existing package map if a command is going to run "pub get" to update the package map (#3202)

Also remove a redundant check for the --pub option in the run command

packages/flutter_tools/lib/src/commands/run.dart

diff --git a/packages/flutter_tools/lib/src/commands/run.dart b/packages/flutter_tools/lib/src/commands/run.dart
index 88ddcb7..e78f11c 100644
--- a/packages/flutter_tools/lib/src/commands/run.dart
+++ b/packages/flutter_tools/lib/src/commands/run.dart
@@ -10,7 +10,6 @@
 import '../application_package.dart';
 import '../base/common.dart';
 import '../build_configuration.dart';
-import '../dart/pub.dart';
 import '../device.dart';
 import '../globals.dart';
 import '../runner/flutter_command.dart';
@@ -83,16 +82,6 @@
   bool get requiresDevice => true;
 
   @override
-  Future<int> run() async {
-    if (argResults['pub']) {
-      int exitCode = await pubGet();
-      if (exitCode != 0)
-        return exitCode;
-    }
-    return await super.run();
-  }
-
-  @override
   Future<int> runInProject() async {
     bool clearLogs = argResults['clear-logs'];
 

packages/flutter_tools/lib/src/runner/flutter_command.dart

diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index 876c832..73bc0c4 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart
@@ -154,10 +154,13 @@
       }
     }
 
-    String error = PackageMap.instance.checkValid();
-    if (error != null) {
-      printError(error);
-      return false;
+    // Validate the current package map only if we will not be running "pub get" later.
+    if (!(_usesPubOption && argResults['pub'])) {
+      String error = PackageMap.instance.checkValid();
+      if (error != null) {
+        printError(error);
+        return false;
+      }
     }
 
     return true;