Move CompilerStats from isolate to thread. Aggregate stats.

runtime/vm/thread.h

Index: runtime/vm/thread.h
diff --git a/runtime/vm/thread.h b/runtime/vm/thread.h
index 31313d6ec1b6398aa00be83e8ac059fbc614db3f..8e126f5337f4267b348cdf2063f0dcad773cfbed 100644
--- a/runtime/vm/thread.h
+++ b/runtime/vm/thread.h
@@ -23,6 +23,7 @@ class Array;
 class CHA;
 class Class;
 class Code;
+class CompilerStats;
 class Error;
 class ExceptionHandlers;
 class Field;
@@ -443,6 +444,8 @@ LEAF_RUNTIME_ENTRY_LIST(DEFINE_OFFSET_METHOD)
   void set_sticky_error(const Error& value);
   void clear_sticky_error();
 
+  CompilerStats* compiler_stats() { return compiler_stats_; }
+
 #if defined(DEBUG)
 #define REUSABLE_HANDLE_SCOPE_ACCESSORS(object)                                \
   void set_reusable_##object##_handle_scope_active(bool value) {               \
@@ -651,6 +654,8 @@ LEAF_RUNTIME_ENTRY_LIST(DECLARE_MEMBERS)
 
   RawError* sticky_error_;
 
+  CompilerStats* compiler_stats_;
+
   // Reusable handles support.
 #define REUSABLE_HANDLE_FIELDS(object)                                         \
   object* object##_handle_;