Make CopyOnWriteBuffer keep capacity

webrtc/base/copyonwritebuffer.h

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 135 matching lines @@
     return cdata()[index];
   }
 
   // Replace the contents of the buffer. Accepts the same types as the
   // constructors.
   template <typename T,
             typename std::enable_if<
                 internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
   void SetData(const T* data, size_t size) {
     RTC_DCHECK(IsConsistent());
-    if (!buffer_ || !buffer_->HasOneRef()) {
-      buffer_ = size > 0 ? new RefCountedObject<Buffer>(data, size)
-                         : nullptr;
+    if (!buffer_) {
+      buffer_ = size > 0 ? new RefCountedObject<Buffer>(data, size) : nullptr;
+    } else if (!buffer_->HasOneRef()) {
+      buffer_ = new RefCountedObject<Buffer>(data, size, buffer_->capacity());
     } else {
       buffer_->SetData(data, size);
     }
     RTC_DCHECK(IsConsistent());
   }
 
   template <typename T,
             size_t N,
             typename std::enable_if<
                 internal::BufferCompat<uint8_t, T>::value>::type* = nullptr>
@@ skipping 77 matching lines @@
       return;
     } else if (capacity <= buffer_->capacity()) {
       return;
     }
 
     CloneDataIfReferenced(std::max(buffer_->capacity(), capacity));
     buffer_->EnsureCapacity(capacity);
     RTC_DCHECK(IsConsistent());
   }
 
-  // Resets the buffer to zero size and capacity.
+  // Resets the buffer to zero size without altering capacity. Works even if the
+  // buffer has been moved from.
   void Clear() {
-    RTC_DCHECK(IsConsistent());
-    if (!buffer_ || !buffer_->HasOneRef()) {
-      buffer_ = nullptr;
+    if (!buffer_)
+      return;
+
+    if (buffer_->HasOneRef()) {
+      buffer_->Clear();
     } else {
-      buffer_->Clear();
+      buffer_ = new RefCountedObject<Buffer>(0, buffer_->capacity());
     }
     RTC_DCHECK(IsConsistent());
   }
 
   // Swaps two buffers.
   friend void swap(CopyOnWriteBuffer& a, CopyOnWriteBuffer& b) {
     std::swap(a.buffer_, b.buffer_);
   }
 
  private:
@@ skipping 14 matching lines @@
     return (!buffer_ || buffer_->capacity() > 0);
   }
 
   // buffer_ is either null, or points to an rtc::Buffer with capacity > 0.
   scoped_refptr<RefCountedObject<Buffer>> buffer_;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_COPYONWRITEBUFFER_H_