Significantly improve performance of code coverage tool by precomputing a map token_pos->line numbe…

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 37119)
+++ runtime/vm/object.h	(working copy)
@@ -2472,6 +2472,7 @@
   RawString* Source() const;
   RawString* GenerateSource() const;  // Generates source code from Tokenstream.
   RawGrowableObjectArray* GenerateLineNumberArray() const;
+  void ComputeTokenPosToLineNumberArray() const;
   RawScript::Kind kind() const {
     return static_cast<RawScript::Kind>(raw_ptr()->kind_);
   }
@@ -2517,6 +2518,8 @@
   void set_source(const String& value) const;
   void set_kind(RawScript::Kind value) const;
   void set_tokens(const TokenStream& value) const;
+  void set_token_pos_to_line_nr(const TypedData& value) const;
+  RawTypedData* token_pos_to_line_nr() const;
 
   static RawScript* New();