Record field initializer stores with simple literals at compile-time.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 37262)
+++ runtime/vm/parser.cc	(working copy)
@@ -3545,7 +3545,7 @@
       // value is not assignable (assuming checked mode and disregarding actual
       // mode), the field value is reset and a kImplicitStaticFinalGetter is
       // created at finalization time.
-      if (field->has_static && (LookaheadToken(1) == Token::kSEMICOLON)) {
+      if (LookaheadToken(1) == Token::kSEMICOLON) {
         has_simple_literal = IsSimpleLiteral(*field->type, &init_value);
       }
       SkipExpr();
@@ -3575,6 +3575,13 @@
       library_.AddFieldMetadata(class_field, field->metadata_pos);
     }
 
+    // Start tracking types for fields with simple initializers in their
+    // definition. This avoids some of the overhead to track this at runtime
+    // and rules out many fields from being unnecessary unboxing candidates.
+    if (!field->has_static && has_initializer && has_simple_literal) {
+      class_field.RecordStore(init_value);
+    }
+
     // For static final fields (this includes static const fields), set value to
     // "uninitialized" and create a kImplicitStaticFinalGetter getter method.
     if (field->has_static && has_initializer) {