Revert of Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

webrtc/base/buffer.h

Index: webrtc/base/buffer.h
diff --git a/webrtc/base/buffer.h b/webrtc/base/buffer.h
index 658b06e75bb7140f121b1dc602e222025eaa8ce3..e9c47ee84e02168b6df52bb5c071613c1c9a9067 100644
--- a/webrtc/base/buffer.h
+++ b/webrtc/base/buffer.h
@@ -50,6 +50,7 @@
 class Buffer {
  public:
   Buffer();                   // An empty buffer.
+  Buffer(const Buffer& buf);  // Copy size and contents of an existing buffer.
   Buffer(Buffer&& buf);       // Move contents from an existing buffer.
 
   // Construct a buffer with the specified number of uninitialized bytes.
@@ -97,6 +98,12 @@
   size_t capacity() const {
     RTC_DCHECK(IsConsistent());
     return capacity_;
+  }
+
+  Buffer& operator=(const Buffer& buf) {
+    if (&buf != this)
+      SetData(buf.data(), buf.size());
+    return *this;
   }
 
   Buffer& operator=(Buffer&& buf) {
@@ -273,8 +280,6 @@
   size_t size_;
   size_t capacity_;
   std::unique_ptr<uint8_t[]> data_;
-
-  RTC_DISALLOW_COPY_AND_ASSIGN(Buffer);
 };
 
 }  // namespace rtc