Reland "Removed default Isolate."

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index b8e4492908a4db9bdd60809eb8124d11a3051cd6..305c683a197178d546a3adf87e47fa69d6dd37e7 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1649,7 +1649,7 @@ int Shell::Main(int argc, char* argv[]) {
     v8::V8::SetArrayBufferAllocator(&array_buffer_allocator);
   }
   int result = 0;
-  Isolate* isolate = Isolate::GetCurrent();
+  Isolate* isolate = Isolate::New();
 #ifndef V8_SHARED
   v8::ResourceConstraints constraints;
   constraints.ConfigureDefaults(i::OS::TotalPhysicalMemory(),
@@ -1659,6 +1659,7 @@ int Shell::Main(int argc, char* argv[]) {
 #endif
   DumbLineEditor dumb_line_editor(isolate);
   {
+    Isolate::Scope scope(isolate);
     Initialize(isolate);
 #ifdef ENABLE_VTUNE_JIT_INTERFACE
     vTune::InitializeVtuneForV8();