Experimental Profiler: tweak type info threshold.

Also included: simplify String.slice.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/9694033

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11021 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -216,7 +216,7 @@ DEFINE_bool(weighted_back_edges, false,
             "weight back edges by jump distance for interrupt triggering")
 DEFINE_int(interrupt_budget, 5900,
            "execution budget before interrupt is triggered")
-DEFINE_int(type_info_threshold, 40,
+DEFINE_int(type_info_threshold, 15,
            "percentage of ICs that must have type info to allow optimization")
 DEFINE_int(self_opt_count, 130, "call count before self-optimization")
 

src/string.js

@@ -554,27 +554,26 @@ function StringSlice(start, end) {
     }
   } else {
     if (start_i > s_len) {
-      start_i = s_len;
+      return '';
     }
   }
 
   if (end_i < 0) {
     end_i += s_len;
     if (end_i < 0) {
-      end_i = 0;
+      return '';
     }
   } else {
     if (end_i > s_len) {
       end_i = s_len;
     }
   }
 
-  var num_c = end_i - start_i;
-  if (num_c < 0) {
-    num_c = 0;
+  if (end_i <= start_i) {
+    return '';
   }
 
-  return SubString(s, start_i, start_i + num_c);
+  return SubString(s, start_i, end_i);
 }