Use multiple shared memory buffers cyclically for audio capture.

content/browser/renderer_host/media/audio_input_renderer_host.cc

Index: content/browser/renderer_host/media/audio_input_renderer_host.cc
===================================================================
--- content/browser/renderer_host/media/audio_input_renderer_host.cc	(revision 185810)
+++ content/browser/renderer_host/media/audio_input_renderer_host.cc	(working copy)
@@ -27,8 +27,8 @@
   // The audio input stream ID in the render view.
   int stream_id;
 
-  // Shared memory for transmission of the audio data.
-  base::SharedMemory shared_memory;
+  // Shared memory buffers for transmission of the audio data.
+  AudioInputSyncWriter::SharedMemoryVector shared_memory;
 
   // The synchronous writer to be used by the controller. We have the
   // ownership of the writer.
@@ -127,15 +127,6 @@
 
   // Once the audio stream is created then complete the creation process by
   // mapping shared memory and sharing with the renderer process.
-  base::SharedMemoryHandle foreign_memory_handle;
-  if (!entry->shared_memory.ShareToProcess(peer_handle(),
-                                           &foreign_memory_handle)) {
-    // If we failed to map and share the shared memory then close the audio
-    // stream and send an error message.
-    DeleteEntryOnError(entry);
-    return;
-  }
-
   AudioInputSyncWriter* writer =
       static_cast<AudioInputSyncWriter*>(entry->writer.get());
 
@@ -152,10 +143,23 @@
     DeleteEntryOnError(entry);
     return;
   }
+  Send(new AudioInputMsg_NotifyStreamCreated(entry->stream_id,
+      foreign_socket_handle,
+      entry->shared_memory.size()));
 
-  Send(new AudioInputMsg_NotifyStreamCreated(entry->stream_id,
-      foreign_memory_handle, foreign_socket_handle,
-      entry->shared_memory.created_size()));
+  for (size_t i = 0; i < entry->shared_memory.size(); ++i) {
+    base::SharedMemoryHandle foreign_memory_handle;
+    if (!entry->shared_memory[i]->ShareToProcess(peer_handle(),
+                                                 &foreign_memory_handle)) {
+      // If we failed to map and share the shared memory then close the audio
+      // stream and send an error message.
+      DeleteEntryOnError(entry);
+      return;
+    }
+    Send(new AudioInputMsg_NotifySharedMemoryCreated(entry->stream_id,
+        foreign_memory_handle,
+        entry->shared_memory[i]->created_size(), i));
+  }
 }
 
 void AudioInputRendererHost::DoSendRecordingMessage(
@@ -209,8 +213,11 @@
 }
 
 void AudioInputRendererHost::OnCreateStream(
-    int stream_id, const media::AudioParameters& params,
-    const std::string& device_id, bool automatic_gain_control) {
+    int stream_id,
+    const media::AudioParameters& params,
+    const std::string& device_id,
+    bool automatic_gain_control,
+    int shared_memory_count) {
   VLOG(1) << "AudioInputRendererHost::OnCreateStream(stream_id="
           << stream_id << ")";
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
@@ -238,10 +245,14 @@
 
   // Create the shared memory and share it with the renderer process
   // using a new SyncWriter object.
-  if (!entry->shared_memory.CreateAndMapAnonymous(mem_size)) {
-    // If creation of shared memory failed then send an error message.
-    SendErrorMessage(stream_id);
-    return;
+  entry->shared_memory.resize(shared_memory_count);
+  for (size_t i = 0; i < entry->shared_memory.size(); ++i) {
+    entry->shared_memory[i] = new base::SharedMemory();
+    if (!entry->shared_memory[i]->CreateAndMapAnonymous(mem_size)) {
+      // If creation of shared memory failed then send an error message.
+      SendErrorMessage(stream_id);
+      return;
+    }
   }
 
   scoped_ptr<AudioInputSyncWriter> writer(