Disk cache: First pass to add support for sparse entries....

net/base/io_buffer.h

Index: net/base/io_buffer.h
===================================================================
--- net/base/io_buffer.h	(revision 18456)
+++ net/base/io_buffer.h	(working copy)
@@ -28,15 +28,50 @@
   char* data_;
 };
 
+// This version stores the size of the buffer so that the creator of the object
+// doesn't have to keep track of that value.
+// NOTE: This doesn't mean that we want to stop sending the size as an explictit
+// argument to IO functions. Please keep using IOBuffer* for API declarations.
+class IOBufferWithSize : public IOBuffer {
+ public:
+  explicit IOBufferWithSize(int size) : IOBuffer(size), size_(size) {}
+  ~IOBufferWithSize() {}
+
+  int size() const { return size_; }
+
+ private:
+  int size_;
+};
+
+// This version allows the caller to do multiple IO operations reusing a given
+// IOBuffer. We don't own data_, we simply make it point to the buffer of the
+// passed in IOBuffer, plus the desired offset.
+class ReusedIOBuffer : public IOBuffer {
+ public:
+  ReusedIOBuffer(IOBuffer* base, int size)
+      : IOBuffer(base->data()), base_(base), size_(size) {}
+  ~ReusedIOBuffer() {
+    // We don't really own a buffer.
+    data_ = NULL;
+  }
+
+  int size() const { return size_; }
+  void SetOffset(int offset);
+
+ private:
+  scoped_refptr<IOBuffer> base_;
+  int size_;
+};
+
 // This class allows the creation of a temporary IOBuffer that doesn't really
 // own the underlying buffer. Please use this class only as a last resort.
 // A good example is the buffer for a synchronous operation, where we can be
 // sure that nobody is keeping an extra reference to this object so the lifetime
 // of the buffer can be completely managed by its intended owner.
-class WrappedIOBuffer : public net::IOBuffer {
+class WrappedIOBuffer : public IOBuffer {
  public:
   explicit WrappedIOBuffer(const char* data)
-      : net::IOBuffer(const_cast<char*>(data)) {}
+      : IOBuffer(const_cast<char*>(data)) {}
   ~WrappedIOBuffer() {
     data_ = NULL;
   }