Show error with gn desc when no matches are made

This tells the user that they input a value that matches nothing
so that they know they need to correct the input and try again
rather than showing no output and acting like the command worked
correctly

Bug: 646012
Change-Id: I9e796a4a09216dde8939e4a60b255f8beff0c52b
Reviewed-on: https://chromium-review.googlesource.com/1037910Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Eli Ribble <eliribble@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555188}

tools/gn/command_desc.cc

@@ -456,6 +456,12 @@ int RunDesc(const std::vector<std::string>& args) {
 
   bool json = cmdline->GetSwitchValueASCII("format") == "json";
 
+  if (target_matches.empty() && config_matches.empty()) {
+    OutputString("The input " + args[1] +
+                 " matches no targets, configs or files.\n", DECORATION_YELLOW);
+    return 1;
+  }
+
   if (json) {
     // Convert all targets/configs to JSON, serialize and print them
     auto res = std::make_unique<base::DictionaryValue>();