Unobscurified OFStream.

Use simple HAS-A relationship instead of obscure multiple inheritance.
In theory, UBSan should be totally happy with this, but it still isn't.
This seems to be a bug in UBSan, see e.g.
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-December/040225.html

BUG=chromium:448102
LOG=y

Review URL: https://codereview.chromium.org/859773002

Cr-Commit-Position: refs/heads/master@{#26139}

src/ostreams.cc

@@ -17,7 +17,7 @@ OFStreamBase::OFStreamBase(FILE* f) : f_(f) {}
 OFStreamBase::~OFStreamBase() {}
 
 
-OFStreamBase::int_type OFStreamBase::sync() {
+int OFStreamBase::sync() {
   std::fflush(f_);
   return 0;
 }
@@ -28,8 +28,15 @@ OFStreamBase::int_type OFStreamBase::overflow(int_type c) {
 }
 
 
-OFStream::OFStream(FILE* f) : OFStreamBase(f), std::ostream(this) {
+std::streamsize OFStreamBase::xsputn(const char* s, std::streamsize n) {
+  return static_cast<std::streamsize>(
+      std::fwrite(s, 1, static_cast<size_t>(n), f_));
+}
+
+
+OFStream::OFStream(FILE* f) : std::ostream(nullptr), buf_(f) {
   DCHECK_NOT_NULL(f);
+  rdbuf(&buf_);
 }
 
 

src/ostreams.h

@@ -17,29 +17,29 @@
 namespace v8 {
 namespace internal {
 
+
 class OFStreamBase : public std::streambuf {
- protected:
+ public:
   explicit OFStreamBase(FILE* f);
   virtual ~OFStreamBase();
 
-  int_type sync() FINAL;
-  int_type overflow(int_type c) FINAL;
-
- private:
+ protected:
   FILE* const f_;
 
-  DISALLOW_COPY_AND_ASSIGN(OFStreamBase);
+  virtual int sync();
+  virtual int_type overflow(int_type c);
+  virtual std::streamsize xsputn(const char* s, std::streamsize n);
 };
 
 
 // An output stream writing to a file.
-class OFStream FINAL : private virtual OFStreamBase, public std::ostream {
+class OFStream : public std::ostream {
  public:
   explicit OFStream(FILE* f);
   ~OFStream();
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(OFStream);
+  OFStreamBase buf_;
 };