VM: Allow configuring use_field_guards on the per-isolate basis and include it into snapshot featur…

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
diff --git a/runtime/vm/dart.cc b/runtime/vm/dart.cc
index 83b1055b308621580006287e09e58a33d60212dd..40dc4986a9a276036c299cfd109aa76055b0ae85 100644
--- a/runtime/vm/dart.cc
+++ b/runtime/vm/dart.cc
@@ -653,7 +653,7 @@ RawError* Dart::InitializeIsolate(const uint8_t* snapshot_data,
 }
 
 
-const char* Dart::FeaturesString(Snapshot::Kind kind) {
+const char* Dart::FeaturesString(Isolate* isolate, Snapshot::Kind kind) {
   TextBuffer buffer(64);
 
 // Different fields are included for DEBUG/RELEASE/PRODUCT.
@@ -667,9 +667,15 @@ const char* Dart::FeaturesString(Snapshot::Kind kind) {
 
   if (Snapshot::IncludesCode(kind)) {
     // Checked mode affects deopt ids.
-    buffer.AddString(FLAG_enable_asserts ? " asserts" : " no-asserts");
-    buffer.AddString(FLAG_enable_type_checks ? " type-checks"
-                                             : " no-type-checks");
+    const bool asserts =
+        (isolate != NULL) ? isolate->asserts() : FLAG_enable_asserts;
+    const bool type_checks =
+        (isolate != NULL) ? isolate->type_checks() : FLAG_enable_type_checks;
+    const bool field_guards =
+        (isolate != NULL) ? isolate->use_field_guards() : FLAG_use_field_guards;
+    buffer.AddString(asserts ? " asserts" : " no-asserts");
+    buffer.AddString(type_checks ? " type-checks" : " no-type-checks");
+    buffer.AddString(field_guards ? "field-guards" : "no-field-guards");
 
 // Generated code must match the host architecture and ABI.
 #if defined(TARGET_ARCH_ARM)