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 eeeafc6ce986d7f85984a8c6f669f1fcc580772c..ac6cc2c559129538575dff760a3e7805a444b55a 100644
--- a/content/browser/renderer_host/media/video_capture_buffer_pool.cc
+++ b/content/browser/renderer_host/media/video_capture_buffer_pool.cc
@@ -72,7 +72,9 @@ class SimpleBufferHandle final : public VideoCaptureBufferPool::BufferHandle {
   }
   ClientBuffer AsClientBuffer() override { return nullptr; }
   base::PlatformFile AsPlatformFile() override {
-#if defined(OS_POSIX)
+#if defined(OS_MACOSX)
+    return handle_.GetFileDescriptor().fd;
+#elif defined(OS_POSIX)
     return handle_.fd;
 #elif defined(OS_WIN)
     return handle_;
@@ -110,7 +112,9 @@ class GpuMemoryBufferBufferHandle
   ClientBuffer AsClientBuffer() override { return gmb_->AsClientBuffer(); }
   base::PlatformFile AsPlatformFile() override {
     DCHECK_EQ(gmb_->GetHandle().type, gfx::SHARED_MEMORY_BUFFER);
-#if defined(OS_POSIX)
+#if defined(OS_MACOSX)
+    return gmb_->GetHandle().handle.GetFileDescriptor().fd;
+#elif defined(OS_POSIX)
     return gmb_->GetHandle().handle.fd;
 #elif defined(OS_WIN)
     return gmb_->GetHandle().handle;