Clean up VMState a little bit.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index e62e6b35e4b6ccccef4588111e3ba69c411ffec1..0d391f79a91546efe149f4b95f20de62f4a7a543 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -627,7 +627,7 @@ Handle<SharedFunctionInfo> Compiler::Compile(Handle<String> source,
   isolate->counters()->total_compile_size()->Increment(source_length);
 
   // The VM is in the COMPILER state until exiting this function.
-  VMState state(isolate, COMPILER);
+  VMState<COMPILER> state(isolate);
 
   CompilationCache* compilation_cache = isolate->compilation_cache();
 
@@ -701,7 +701,7 @@ Handle<SharedFunctionInfo> Compiler::CompileEval(Handle<String> source,
   isolate->counters()->total_compile_size()->Increment(source_length);
 
   // The VM is in the COMPILER state until exiting this function.
-  VMState state(isolate, COMPILER);
+  VMState<COMPILER> state(isolate);
 
   // Do a lookup in the compilation cache; if the entry is not there, invoke
   // the compiler and add the result to the cache.
@@ -864,7 +864,7 @@ bool Compiler::CompileLazy(CompilationInfo* info) {
   ZoneScope zone_scope(info->zone(), DELETE_ON_EXIT);
 
   // The VM is in the COMPILER state until exiting this function.
-  VMState state(isolate, COMPILER);
+  VMState<COMPILER> state(isolate);
 
   PostponeInterruptsScope postpone(isolate);
 
@@ -928,7 +928,7 @@ void Compiler::RecompileParallel(Handle<JSFunction> closure) {
   }
 
   SmartPointer<CompilationInfo> info(new CompilationInfoWithZone(closure));
-  VMState state(isolate, PARALLEL_COMPILER);
+  VMState<COMPILER> state(isolate);
   PostponeInterruptsScope postpone(isolate);
 
   Handle<SharedFunctionInfo> shared = info->shared_info();
@@ -1003,7 +1003,7 @@ void Compiler::InstallOptimizedCode(OptimizingCompiler* optimizing_compiler) {
   }
 
   Isolate* isolate = info->isolate();
-  VMState state(isolate, PARALLEL_COMPILER);
+  VMState<COMPILER> state(isolate);
   Logger::TimerEventScope timer(
       isolate, Logger::TimerEventScope::v8_recompile_synchronous);
   // If crankshaft succeeded, install the optimized code else install