Add strong mode.

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 83fa2fa720e7b660034d84df15ee9a3c4a2e18cb..761a85d011f10a43c15d0e3ef2bd1ba5d38c4eb0 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -227,25 +227,47 @@ template <typename T, class P = FreeStoreAllocationPolicy> class List;
 
 enum LanguageMode {
   // LanguageMode is expressed as a bitmask. Descriptions of the bits:
-  STRICT = 1 << 0,
+  STRICT_BIT = 1 << 0,
+  STRONG_BIT = 1 << 1,
   LANGUAGE_END,
 
   // Shorthands for some common language modes.
-  SLOPPY = 0
+  SLOPPY = 0,
+  STRICT = STRICT_BIT,
+  STRONG = STRICT_BIT | STRONG_BIT
 };
 
+
+inline bool is_sloppy(LanguageMode language_mode) {
+  return (language_mode & STRICT_BIT) == 0;
+}
+
+
 inline bool is_strict(LanguageMode language_mode) {
-  return language_mode & STRICT;
+  return language_mode & STRICT_BIT;
 }
 
-inline bool is_sloppy(LanguageMode language_mode) {
-  return (language_mode & STRICT) == 0;
+
+inline bool is_strong(LanguageMode language_mode) {
+  return language_mode & STRONG_BIT;
 }
 
+
 inline bool is_valid_language_mode(int language_mode) {
-  return language_mode == SLOPPY || language_mode == STRICT;
+  return language_mode == SLOPPY || language_mode == STRICT ||
+         language_mode == STRONG;
+}
+
+
+inline LanguageMode construct_language_mode(bool strict_bit, bool strong_bit) {
+  int language_mode = 0;
+  if (strict_bit) language_mode |= STRICT_BIT;
+  if (strong_bit) language_mode |= STRONG_BIT;
+  DCHECK(is_valid_language_mode(language_mode));
+  return static_cast<LanguageMode>(language_mode);
 }
 
+
 // Mask for the sign bit in a smi.
 const intptr_t kSmiSignMask = kIntptrSignBit;