[builtins] Move StringStartsWith to a C++ builtin.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 7d41719eca8b4eb9b53d9060c92f3348642155d9..0c41e6653c45126347f5f75c327acbf958b50d25 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1453,6 +1453,8 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
                           2, true);
     SimpleInstallFunction(prototype, "substring",
                           Builtins::kStringPrototypeSubstring, 2, true);
+    SimpleInstallFunction(prototype, "startsWith",
+                          Builtins::kStringPrototypeStartsWith, 1, false);
     SimpleInstallFunction(prototype, "toString",
                           Builtins::kStringPrototypeToString, 0, true);
     SimpleInstallFunction(prototype, "trim", Builtins::kStringPrototypeTrim, 0,