AK: Allow specifying writability of a FixedMemoryStream

AK/MemoryStream.cpp

@@ -12,8 +12,9 @@
 
 namespace AK {
 
-FixedMemoryStream::FixedMemoryStream(Bytes bytes)
+FixedMemoryStream::FixedMemoryStream(Bytes bytes, bool writing_enabled)
     : m_bytes(bytes)
+    , m_writing_enabled(writing_enabled)
 {
 }
 

AK/MemoryStream.h

@@ -16,7 +16,7 @@ namespace AK {
 /// using a single read/write head.
 class FixedMemoryStream : public SeekableStream {
 public:
-    explicit FixedMemoryStream(Bytes bytes);
+    explicit FixedMemoryStream(Bytes bytes, bool writing_enabled = true);
     explicit FixedMemoryStream(ReadonlyBytes bytes);
 
     virtual bool is_eof() const override;