Fix data races caused by compiler stats counters in the parser.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 27120)
+++ runtime/vm/parser.cc	(working copy)
@@ -64,7 +64,7 @@
       indent_++;
     }
   }
-  ~TraceParser() { indent_--; }
+  ~TraceParser() { if (FLAG_trace_parser) indent_--; }
  private:
   void PrintIndent() {
     for (int i = 0; i < indent_; i++) { OS::Print(". "); }
@@ -345,7 +345,9 @@
 
 void Parser::SetPosition(intptr_t position) {
   if (position < TokenPos() && position != 0) {
-    CompilerStats::num_tokens_rewind += (TokenPos() - position);
+    if (FLAG_compiler_stats) {
+      CompilerStats::num_tokens_rewind += (TokenPos() - position);
+    }
   }
   tokens_iterator_.SetCurrentPosition(position);
   token_kind_ = Token::kILLEGAL;
@@ -368,14 +370,18 @@
       ErrorMsg(TokenPos(), "%s", CurrentLiteral()->ToCString());
     }
   }
-  CompilerStats::num_token_checks++;
+  if (FLAG_compiler_stats) {
+    CompilerStats::num_token_checks++;
+  }
   return token_kind_;
 }
 
 
 Token::Kind Parser::LookaheadToken(int num_tokens) {
-  CompilerStats::num_tokens_lookahead++;
-  CompilerStats::num_token_checks++;
+  if (FLAG_compiler_stats) {
+    CompilerStats::num_tokens_lookahead++;
+    CompilerStats::num_token_checks++;
+  }
   return tokens_iterator_.LookaheadTokenKind(num_tokens);
 }