Add better consistency check and error output to plot script.

tools/profviz/stdio.js

Index: tools/profviz/stdio.js
diff --git a/tools/profviz/stdio.js b/tools/profviz/stdio.js
index e8001494c9df641ffbb0cfce90f618ca729339f0..db38f042a7d016efb95e9d6803e8f59593920c83 100644
--- a/tools/profviz/stdio.js
+++ b/tools/profviz/stdio.js
@@ -44,7 +44,11 @@ if (!isNaN(range_end)) range_end_override = range_end;
 
 var kResX = 1600;
 var kResY = 600;
-var psc = new PlotScriptComposer(kResX, kResY);
+function log_error(text) {
+  print(text);
+  quit(1);
+}
+var psc = new PlotScriptComposer(kResX, kResY, log_error);
 psc.collectData(readline, distortion_per_entry);
 psc.findPlotRange(range_start_override, range_end_override);
 print("set terminal pngcairo size " + kResX + "," + kResY +