[Interpreter] Fixes VisitNewLocalBlockContext to reserve consecutive registers.

VisitNewLocalBlockContext funciton was allocating two registers and checking
if they are consecutive. This cl changes it to reserve consecutive registers.
The earlier code breaks this test mjsunit/regress/regress-542099.js.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1545003003

Cr-Commit-Position: refs/heads/master@{#33086}

src/interpreter/bytecode-generator.cc

@@ -2074,9 +2074,10 @@ void BytecodeGenerator::VisitNewLocalBlockContext(Scope* scope) {
 
   // Allocate a new local block context.
   TemporaryRegisterScope temporary_register_scope(builder());
-  Register scope_info = temporary_register_scope.NewRegister();
-  Register closure = temporary_register_scope.NewRegister();
-  DCHECK(Register::AreContiguous(scope_info, closure));
+  temporary_register_scope.PrepareForConsecutiveAllocations(2);
+  Register scope_info = temporary_register_scope.NextConsecutiveRegister();
+  Register closure = temporary_register_scope.NextConsecutiveRegister();
+
   builder()
       ->LoadLiteral(scope->GetScopeInfo(isolate()))
       .StoreAccumulatorInRegister(scope_info);