[stubs] Port String.prototype.substring to TurboFan

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 42a064c823aee39503716702bc1d4c0dd6886adc..922f37aa611a8d1bec458bf5465c0ddeb1e1a7f8 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1408,6 +1408,8 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
                           Builtins::kStringPrototypeLocaleCompare, 1, true);
     SimpleInstallFunction(prototype, "normalize",
                           Builtins::kStringPrototypeNormalize, 0, false);
+    SimpleInstallFunction(prototype, "substring",
+                          Builtins::kStringPrototypeSubstring, 2, true);
     SimpleInstallFunction(prototype, "toString",
                           Builtins::kStringPrototypeToString, 0, true);
     SimpleInstallFunction(prototype, "trim", Builtins::kStringPrototypeTrim, 0,