Bug 1294940 - Part 1: Add ConstUTF8CharsZ class for const UTF8 string. r=jwalden

--HG--
extra : rebase_source : 6f8b433038c1db36902aaeba1c7f5694bf5900a5

js/public/CharacterEncoding.h

@@ -109,6 +109,33 @@ class UTF8CharsZ : public mozilla::RangedPtr<unsigned char>
     char* c_str() { return reinterpret_cast<char*>(get()); }
 };
 
+/*
+ * A wrapper for a "const char*" that is encoded using UTF-8.
+ * This class does not manage ownership of the data; that is left
+ * to others.  This differs from UTF8CharsZ in that the chars are
+ * const and it allows assignment.
+ */
+class ConstUTF8CharsZ
+{
+    const char* data_;
+
+  public:
+    ConstUTF8CharsZ() : data_(nullptr)
+    {}
+
+    ConstUTF8CharsZ(const char* aBytes, size_t aLength)
+      : data_(aBytes)
+    {
+        MOZ_ASSERT(aBytes[aLength] == '\0');
+    }
+
+    const void* get() const { return data_; }
+
+    const char* c_str() const { return data_; }
+
+    explicit operator bool() const { return data_ != nullptr; }
+};
+
 /*
  * SpiderMonkey uses a 2-byte character representation: it is a
  * 2-byte-at-a-time view of a UTF-16 byte stream. This is similar to UCS-2,