Move global V8::UseCrankshaft() into the Isolate.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 0e7b6d55d1521965efb3c4b7a04974e66c19d3cd..bcccae498411394604611ccc8879ea3c4b319c53 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1792,6 +1792,7 @@ Isolate::Isolate()
       regexp_stack_(NULL),
       date_cache_(NULL),
       code_stub_interface_descriptors_(NULL),
+      use_crankshaft_(true),
       initialized_from_snapshot_(false),
       cpu_profiler_(NULL),
       heap_profiler_(NULL),
@@ -2147,6 +2148,10 @@ bool Isolate::Init(Deserializer* des) {
 
   stress_deopt_count_ = FLAG_deopt_every_n_times;
 
+  use_crankshaft_ = FLAG_crankshaft
+      && !Serializer::enabled()
+      && CPU::SupportsCrankshaft();
+
   if (function_entry_hook() != NULL) {
     // When function entry hooking is in effect, we have to create the code
     // stubs from scratch to get entry hooks, rather than loading the previously