Fixed compilation time measurement, restructure some code.

runtime/vm/timer.h

Index: runtime/vm/timer.h
===================================================================
--- runtime/vm/timer.h	(revision 7417)
+++ runtime/vm/timer.h	(working copy)
@@ -39,10 +39,9 @@
   }
 
   // Get total cummulative elapsed time in micros and reset the counters.

[hausner, 2012/05/08 21:41:01]

Please adjust the comment. I think this was originally Siva's code, so me have
an answer as to why the Reset was here. 

[srdjan, 2012/05/08 21:51:31]

Done.

-  int64_t TotalElapsedTime() {
+  int64_t TotalElapsedTime() const {
     if (enabled_) {
       int64_t result = total_;
-      Reset();
       return result;
     }
     return 0;
@@ -140,10 +139,10 @@
 //   code that needs to be timed.
 //   ....
 // }
-class TimerScope : public ValueObject {
+class TimerScope : public StackResource {
  public:
-  TimerScope(bool flag, Timer* timer)
-      : flag_(flag), nested_(false), timer_(timer) {
+  TimerScope(bool flag, Timer* timer, BaseIsolate* isolate = NULL)
+      : StackResource(isolate), flag_(flag), nested_(false), timer_(timer) {
     if (flag_) {
       if (!timer_->running()) {
         timer_->Start();