Forward capturer id from desktop process to network process

Updates of message, proxy and agent are needed to forward capturer id to the
network process and eventually to the client.

BUG=chromium:679523, chromium:650926

Review-Url: https://codereview.chromium.org/2848753002
Cr-Commit-Position: refs/heads/master@{#467902}

remoting/host/chromoting_messages.h

@@ -167,6 +167,9 @@ IPC_STRUCT_BEGIN(SerializedDesktopFrame)
 
   // DPI for this frame.
   IPC_STRUCT_MEMBER(webrtc::DesktopVector, dpi)
+
+  // Capturer Id
+  IPC_STRUCT_MEMBER(uint32_t, capturer_id)
 IPC_STRUCT_END()
 
 IPC_ENUM_TRAITS_MAX_VALUE(webrtc::DesktopCapturer::Result,

remoting/host/desktop_session_agent.cc

@@ -320,6 +320,7 @@ void DesktopSessionAgent::OnCaptureResult(
     serialized_frame.dimensions = frame->size();
     serialized_frame.capture_time_ms = frame->capture_time_ms();
     serialized_frame.dpi = frame->dpi();
+    serialized_frame.capturer_id = frame->capturer_id();
     for (webrtc::DesktopRegion::Iterator i(frame->updated_region());
          !i.IsAtEnd(); i.Advance()) {
       serialized_frame.dirty_region.push_back(i.rect());

remoting/host/desktop_session_proxy.cc

@@ -482,6 +482,7 @@ void DesktopSessionProxy::OnCaptureResult(
           new IpcSharedBuffer(shared_buffer_core)));
   frame->set_capture_time_ms(serialized_frame.capture_time_ms);
   frame->set_dpi(serialized_frame.dpi);
+  frame->set_capturer_id(serialized_frame.capturer_id);
 
   for (const auto& rect : serialized_frame.dirty_region) {
     frame->mutable_updated_region()->AddRect(rect);