Concat help strings and print in one go

Compilers don't flatten os << const char* for you. Save a bit binary size.

Bug:NO

Change-Id: Iabe0de83fdf6394f223d0423e63bd5aadf1453b3
Reviewed-on: https://chromium-review.googlesource.com/503829Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Loo Rong Jie <loorongjie@gmail.com>
Cr-Commit-Position: refs/heads/master@{#45272}

src/flags.cc

@@ -575,18 +575,19 @@ void FlagList::PrintHelp() {
 
   OFStream os(stdout);
   os << "Usage:\n"
-     << "  shell [options] -e string\n"
-     << "    execute string in V8\n"
-     << "  shell [options] file1 file2 ... filek\n"
-     << "    run JavaScript scripts in file1, file2, ..., filek\n"
-     << "  shell [options]\n"
-     << "  shell [options] --shell [file1 file2 ... filek]\n"
-     << "    run an interactive JavaScript shell\n"
-     << "  d8 [options] file1 file2 ... filek\n"
-     << "  d8 [options]\n"
-     << "  d8 [options] --shell [file1 file2 ... filek]\n"
-     << "    run the new debugging shell\n\n"
-     << "Options:\n";
+        "  shell [options] -e string\n"
+        "    execute string in V8\n"
+        "  shell [options] file1 file2 ... filek\n"
+        "    run JavaScript scripts in file1, file2, ..., filek\n"
+        "  shell [options]\n"
+        "  shell [options] --shell [file1 file2 ... filek]\n"
+        "    run an interactive JavaScript shell\n"
+        "  d8 [options] file1 file2 ... filek\n"
+        "  d8 [options]\n"
+        "  d8 [options] --shell [file1 file2 ... filek]\n"
+        "    run the new debugging shell\n\n"
+        "Options:\n";
+
   for (size_t i = 0; i < num_flags; ++i) {
     Flag* f = &flags[i];
     os << "  --" << f->name() << " (" << f->comment() << ")\n"