Adjust help message.

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 4126cbcdda96ae49f7d519f72bba4d257b342205..c953b625dfeba5180a32e44ff605cab9a6622cc0 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -963,6 +963,13 @@ static void PrintUsage() {
 "      --warn-on-pause-with-no-debugger\n"
 "  This set is subject to change.\n"
 "  Please see these options (--help --verbose) for further documentation.\n"
+"--snapshot-kind=<snapsot_kind>\n"
+"--snapshot=<file_name>\n"
+"  These snapshot options are used to generate a snapshot of the loaded\n"
+"  Dart script:\n"
+"    <snapshot-kind> controls the kind of snapshot, it could be\n"
+"                    script(default), app-aot or app-jit\n"
+"    <file_name> specifies the file into which the snapshot is written\n"
 "--version\n"
 "  Print the VM version.\n");
   } else {
@@ -987,12 +994,16 @@ static void PrintUsage() {
 "      --warn-on-pause-with-no-debugger\n"
 "  This set is subject to change.\n"
 "  Please see these options for further documentation.\n"
+"--snapshot-kind=<snapsot_kind>\n"
+"--snapshot=<file_name>\n"
+"  These snapshot options are used to generate a snapshot of the loaded\n"
+"  Dart script:\n"
+"    <snapshot-kind> controls the kind of snapshot, it could be\n"
+"                    script(default), app-aot or app-jit\n"
+"    <file_name> specifies the file into which the snapshot is written\n"
 "--version\n"
 "  Print the VM version.\n"
 "\n"
-"--snapshot=<file_name>\n"
-"  loads Dart script and generates a snapshot in the specified file\n"
-"\n"
 "--trace-loading\n"
 "  enables tracing of library and script loading\n"
 "\n"