Update the gen command to not fail on generator flags.

R=vardhan@google.com, vardhan

Review URL: https://codereview.chromium.org/1893683003 .

mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart

diff --git a/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart b/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
index f14216e..362d849 100644
--- a/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
+++ b/mojo/dart/packages/_mojo_for_test_only/lib/test/echo_service.mojom.dart
@@ -765,7 +765,7 @@
   // serializedRuntimeTypeInfo contains the bytes of the Mojo serialization of
   // a mojom_types.RuntimeTypeInfo struct describing the Mojom types in this
   // file. The string contains the base64 encoding of the gzip-compressed bytes.
-  var serializedRuntimeTypeInfo = "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";
+  var serializedRuntimeTypeInfo = "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";
 
   // Deserialize RuntimeTypeInfo
   var bytes = BASE64.decode(serializedRuntimeTypeInfo);

mojo/public/tools/bindings/mojom_tool/bin/linux64/mojom.sha1

diff --git a/mojo/public/tools/bindings/mojom_tool/bin/linux64/mojom.sha1 b/mojo/public/tools/bindings/mojom_tool/bin/linux64/mojom.sha1
index 89139de..4a64bfb 100644
--- a/mojo/public/tools/bindings/mojom_tool/bin/linux64/mojom.sha1
+++ b/mojo/public/tools/bindings/mojom_tool/bin/linux64/mojom.sha1
@@ -1 +1 @@
-97d3c0504e6981432d57572bb57638780826e525
\ No newline at end of file
+75ef97b69d8f912559e7a71593b522fc35a1b33f
\ No newline at end of file

mojo/public/tools/bindings/mojom_tool/bin/mac64/mojom.sha1

diff --git a/mojo/public/tools/bindings/mojom_tool/bin/mac64/mojom.sha1 b/mojo/public/tools/bindings/mojom_tool/bin/mac64/mojom.sha1
index 24f860f..322d728 100644
--- a/mojo/public/tools/bindings/mojom_tool/bin/mac64/mojom.sha1
+++ b/mojo/public/tools/bindings/mojom_tool/bin/mac64/mojom.sha1
@@ -1 +1 @@
-89fed644ffdfd6018f65dc131285c23e16c04429
\ No newline at end of file
+662c32e4dc539a600c8091293f5d8f578c48b70b
\ No newline at end of file

mojom/mojom_parser/gen_cmd.go

diff --git a/mojom/mojom_parser/gen_cmd.go b/mojom/mojom_parser/gen_cmd.go
index 8689c33..7a8c074 100644
--- a/mojom/mojom_parser/gen_cmd.go
+++ b/mojom/mojom_parser/gen_cmd.go
@@ -97,7 +97,9 @@
 			"use --gen-arg-arg=value. To pass --arg, you would use --gen-arg-arg.\n")
 	}
 
-	if err := flagSet.Parse(args[2:]); err != nil {
+	// If err is not ErrHelp, the only way to figure out what it was is to look at
+	// the message provided for users.
+	if err := flagSet.Parse(args[2:]); err != nil && !strings.HasPrefix(err.Error(), "flag provided but not defined") {
 		if err != flag.ErrHelp {
 			fmt.Fprintln(os.Stderr, err.Error())
 		}