Make SharedMemoryHandle a class on Mac.

content/browser/renderer_host/media/video_capture_buffer_pool.cc

Index: content/browser/renderer_host/media/video_capture_buffer_pool.cc
diff --git a/content/browser/renderer_host/media/video_capture_buffer_pool.cc b/content/browser/renderer_host/media/video_capture_buffer_pool.cc
index 70195ba669ac859e202cb70fe184642023eef927..23a63730fd9498c306e1296b1299e132f2ad26b0 100644
--- a/content/browser/renderer_host/media/video_capture_buffer_pool.cc
+++ b/content/browser/renderer_host/media/video_capture_buffer_pool.cc
@@ -70,7 +70,11 @@ class SimpleBufferHandle final : public VideoCaptureBufferPool::BufferHandle {
   ClientBuffer AsClientBuffer() override { return nullptr; }
 #if defined(OS_POSIX)
   base::FileDescriptor AsPlatformFile() override {
+#if defined(OS_MACOSX)
+    return handle_.GetFileDescriptor();
+#else
     return handle_;
+#endif  // defined(OS_MACOSX)
   }
 #endif
 
@@ -102,7 +106,11 @@ class GpuMemoryBufferBufferHandle
   ClientBuffer AsClientBuffer() override { return gmb_->AsClientBuffer(); }
 #if defined(OS_POSIX)
   base::FileDescriptor AsPlatformFile() override {
+#if defined(OS_MACOSX)
+    return gmb_->GetHandle().handle.GetFileDescriptor();
+#else
     return gmb_->GetHandle().handle;
+#endif  // defined(OS_MACOSX)
   }
 #endif