Add flags to force or prevent setting of isolate.is_memory_constrained.

src/flags.cc

Index: src/flags.cc
diff --git a/src/flags.cc b/src/flags.cc
index 4e18cc8c80832b5b1217424acecfa9e9c3578190..5ad0ee0e625ee23023b960fc66c6b30b79272083 100644
--- a/src/flags.cc
+++ b/src/flags.cc
@@ -55,7 +55,8 @@ namespace {
 // to the actual flag, default value, comment, etc.  This is designed to be POD
 // initialized as to avoid requiring static constructors.
 struct Flag {
-  enum FlagType { TYPE_BOOL, TYPE_INT, TYPE_FLOAT, TYPE_STRING, TYPE_ARGS };
+  enum FlagType { TYPE_BOOL, TYPE_MAYBE_BOOL, TYPE_INT, TYPE_FLOAT,
+                  TYPE_STRING, TYPE_ARGS };
 
   FlagType type_;           // What type of flag, bool, int, or string.
   const char* name_;        // Name of the flag, ex "my_flag".
@@ -75,6 +76,11 @@ struct Flag {
     return reinterpret_cast<bool*>(valptr_);
   }
 
+  Maybe<bool>* maybe_bool_variable() const {
+    ASSERT(type_ == TYPE_MAYBE_BOOL);
+    return reinterpret_cast<Maybe<bool>*>(valptr_);
+  }
+
   int* int_variable() const {
     ASSERT(type_ == TYPE_INT);
     return reinterpret_cast<int*>(valptr_);
@@ -133,6 +139,8 @@ struct Flag {
     switch (type_) {
       case TYPE_BOOL:
         return *bool_variable() == bool_default();
+      case TYPE_MAYBE_BOOL:
+        return maybe_bool_variable()->has_value == false;
       case TYPE_INT:
         return *int_variable() == int_default();
       case TYPE_FLOAT:
@@ -157,6 +165,9 @@ struct Flag {
       case TYPE_BOOL:
         *bool_variable() = bool_default();
         break;
+      case TYPE_MAYBE_BOOL:
+        *maybe_bool_variable() = Maybe<bool>();
+        break;
       case TYPE_INT:
         *int_variable() = int_default();
         break;
@@ -186,6 +197,7 @@ const size_t num_flags = sizeof(flags) / sizeof(*flags);
 static const char* Type2String(Flag::FlagType type) {
   switch (type) {
     case Flag::TYPE_BOOL: return "bool";
+    case Flag::TYPE_MAYBE_BOOL: return "maybe_bool";
     case Flag::TYPE_INT: return "int";
     case Flag::TYPE_FLOAT: return "float";
     case Flag::TYPE_STRING: return "string";
@@ -203,6 +215,11 @@ static SmartArrayPointer<const char> ToString(Flag* flag) {
     case Flag::TYPE_BOOL:
       buffer.Add("%s", (*flag->bool_variable() ? "true" : "false"));
       break;
+    case Flag::TYPE_MAYBE_BOOL:
+      buffer.Add("%s", flag->maybe_bool_variable()->has_value
+                       ? (flag->maybe_bool_variable()->value ? "true" : "false")
+                       : "unset");
+      break;
     case Flag::TYPE_INT:
       buffer.Add("%d", *flag->int_variable());
       break;
@@ -380,6 +397,7 @@ int FlagList::SetFlagsFromCommandLine(int* argc,
 
       // if we still need a flag value, use the next argument if available
       if (flag->type() != Flag::TYPE_BOOL &&
+          flag->type() != Flag::TYPE_MAYBE_BOOL &&
           flag->type() != Flag::TYPE_ARGS &&
           value == NULL) {
         if (i < *argc) {
@@ -399,6 +417,9 @@ int FlagList::SetFlagsFromCommandLine(int* argc,
         case Flag::TYPE_BOOL:
           *flag->bool_variable() = !is_bool;
           break;
+        case Flag::TYPE_MAYBE_BOOL:
+          *flag->maybe_bool_variable() = Maybe<bool>(!is_bool);
+          break;
         case Flag::TYPE_INT:
           *flag->int_variable() = strtol(value, &endp, 10);  // NOLINT
           break;
@@ -425,8 +446,9 @@ int FlagList::SetFlagsFromCommandLine(int* argc,
       }
 
       // handle errors
-      if ((flag->type() == Flag::TYPE_BOOL && value != NULL) ||
-          (flag->type() != Flag::TYPE_BOOL && is_bool) ||
+      bool is_bool_type = flag->type() == Flag::TYPE_BOOL ||
+          flag->type() == Flag::TYPE_MAYBE_BOOL;
+      if ((is_bool_type && value != NULL) || (!is_bool_type && is_bool) ||
           *endp != '\0') {
         PrintF(stderr, "Error: illegal value for flag %s of type %s\n"
                "Try --help for options\n",
@@ -549,6 +571,7 @@ void FlagList::PrintHelp() {
 }
 
 
+// static
 void FlagList::EnforceFlagImplications() {
 #define FLAG_MODE_DEFINE_IMPLICATIONS
 #include "flag-definitions.h"