Make stdin blocking when using Stdin::readByte and readLine.

runtime/bin/stdin_linux.cc

Index: runtime/bin/stdin_linux.cc
diff --git a/runtime/bin/stdin_linux.cc b/runtime/bin/stdin_linux.cc
index 43e9e784c493e92315ad47cee49e4e1f9667b62a..4f951987c9819ad3cf4bbd099bd0eb7de59affb4 100644
--- a/runtime/bin/stdin_linux.cc
+++ b/runtime/bin/stdin_linux.cc
@@ -8,16 +8,19 @@
 #include <termios.h>  // NOLINT
 
 #include "bin/stdin.h"
+#include "bin/fdutils.h"
 
 
 namespace dart {
 namespace bin {
 
 int Stdin::ReadByte() {
+  FDUtils::SetBlocking(fileno(stdin));
   int c = getchar();
   if (c == EOF) {
     c = -1;
   }
+  FDUtils::SetNonBlocking(fileno(stdin));
   return c;
 }