Initial UserTag and dart:profiler library

runtime/vm/tags.h

Index: runtime/vm/tags.h
diff --git a/runtime/vm/tags.h b/runtime/vm/tags.h
index de0468f7d5f3db80255a3a9c2bc06318b1d82b3d..9bf0da81f9e7cb33e569514c19398f986f1ce74f 100644
--- a/runtime/vm/tags.h
+++ b/runtime/vm/tags.h
@@ -21,7 +21,6 @@ class JSONObject;
   V(GCOldSpace)                                                                \
   V(RuntimeNative)                                                             \
 
-
 class VMTag : public AllStatic {
  public:
   enum VMTagId {
@@ -33,6 +32,9 @@ class VMTag : public AllStatic {
     kNumVMTags,
   };
 
+  static bool IsVMTag(uword id) {
+    return (id != kInvalidTagId) && (id < kNumVMTags);
+  }
   static const char* TagName(uword id);
 
  private:
@@ -70,6 +72,17 @@ class VMTagCounters {
   int64_t counters_[VMTag::kNumVMTags];
 };
 
+
+class UserTagHelper : public AllStatic {
+ public:
+  static const intptr_t kNoUserTag = 0;
+  // UserTag id space: [kUserTagIdOffset, kUserTagIdOffset + kMaxUserTags).
+  static const intptr_t kMaxUserTags = 64;
+  static const intptr_t kUserTagIdOffset = 0x4096;
+  static const char* TagName(uword tag);
+};
+
+
 }  // namespace dart
 
 #endif  // VM_TAGS_H_