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

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
===================================================================
--- runtime/vm/raw_object_snapshot.cc	(revision 37119)
+++ runtime/vm/raw_object_snapshot.cc	(working copy)
@@ -958,6 +958,9 @@
   TokenStream& stream = TokenStream::Handle();
   stream ^= reader->ReadObjectImpl();
   script.set_tokens(stream);
+  TypedData& array = TypedData::Handle();
+  array ^= reader->ReadObjectImpl();
+  script.set_token_pos_to_line_nr(array);
 
   script.raw_ptr()->line_offset_ = reader->Read<int32_t>();
   script.raw_ptr()->col_offset_ = reader->Read<int32_t>();
@@ -986,6 +989,7 @@
   // Write out all the object pointer fields.
   writer->WriteObjectImpl(ptr()->url_);
   writer->WriteObjectImpl(ptr()->tokens_);
+  writer->WriteObjectImpl(ptr()->token_pos_to_line_nr_);
 
   writer->Write<int32_t>(ptr()->line_offset_);
   writer->Write<int32_t>(ptr()->col_offset_);