Use multiple shared memory buffers cyclically for audio capture.

content/browser/renderer_host/media/audio_input_sync_writer.cc

Index: content/browser/renderer_host/media/audio_input_sync_writer.cc
===================================================================
--- content/browser/renderer_host/media/audio_input_sync_writer.cc	(revision 186213)
+++ content/browser/renderer_host/media/audio_input_sync_writer.cc	(working copy)
@@ -11,8 +11,9 @@
 
 namespace content {
 
-AudioInputSyncWriter::AudioInputSyncWriter(base::SharedMemory* shared_memory)
-    : shared_memory_(shared_memory) {
+AudioInputSyncWriter::AudioInputSyncWriter(SharedMemoryVector* shared_memory)
+    : shared_memory_(shared_memory),
+      current_buffer_id_(0) {
 }
 
 AudioInputSyncWriter::~AudioInputSyncWriter() {}
@@ -20,12 +21,19 @@
 // TODO(henrika): Combine into one method (including Write).
 void AudioInputSyncWriter::UpdateRecordedBytes(uint32 bytes) {
   socket_->Send(&bytes, sizeof(bytes));
+  // There are multiple buffers of shared memory used to transfer recorded
+  // data. Each time, one buffer is used. Both data size and buffer id need
+  // to be sent to the receiver.
+  uint32 index = static_cast<uint32>(current_buffer_id_);
+  socket_->Send(&index, sizeof(index));
+  if (++current_buffer_id_ >= shared_memory_->size())
+    current_buffer_id_ = 0;
 }
 
 uint32 AudioInputSyncWriter::Write(const void* data, uint32 size,
                                    double volume) {
-  media::AudioInputBuffer* buffer =
-      reinterpret_cast<media::AudioInputBuffer*>(shared_memory_->memory());
+  media::AudioInputBuffer* buffer = reinterpret_cast<media::AudioInputBuffer*>(
+      (*shared_memory_)[current_buffer_id_]->memory());
   buffer->params.volume = volume;
   buffer->params.size = size;
   memcpy(buffer->audio, data, size);