Add isolate tag-profile and better handling of errors

runtime/vm/tags.h

Index: runtime/vm/tags.h
diff --git a/runtime/vm/tags.h b/runtime/vm/tags.h
index 98be468cbf79bc429aedceb4b9960f9bcf593758..de0468f7d5f3db80255a3a9c2bc06318b1d82b3d 100644
--- a/runtime/vm/tags.h
+++ b/runtime/vm/tags.h
@@ -7,18 +7,19 @@
 
 #include "vm/allocation.h"
 
-class Isolate;
-
 namespace dart {
 
+class Isolate;
+class JSONObject;
+
 #define VM_TAG_LIST(V)                                                         \
+  V(Idle)                                                                      \
   V(VM) /* Catch all */                                                        \
   V(Compile)                                                                   \
   V(Script)                                                                    \
   V(GCNewSpace)                                                                \
   V(GCOldSpace)                                                                \
   V(RuntimeNative)                                                             \
-  V(Idle)                                                                      \
 
 
 class VMTag : public AllStatic {
@@ -42,6 +43,7 @@ class VMTag : public AllStatic {
   static TagEntry entries_[];
 };
 
+
 class VMTagScope : StackResource {
  public:
   VMTagScope(Isolate* isolate, uword tag);
@@ -53,6 +55,21 @@ class VMTagScope : StackResource {
   DISALLOW_IMPLICIT_CONSTRUCTORS(VMTagScope);
 };
 
+
+class VMTagCounters {
+ public:
+  VMTagCounters();
+
+  void Increment(uword tag);
+
+  int64_t count(uword tag);
+
+  void PrintToJSONObject(JSONObject* obj);
+
+ private:
+  int64_t counters_[VMTag::kNumVMTags];
+};
+
 }  // namespace dart
 
 #endif  // VM_TAGS_H_