media: update comment about shared region

Change-Id: Ib5223719a273db3025e7352fedd2a32b690d00af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697621
Auto-Submit: Matthew Cary (CET) <mattcary@chromium.org>
Reviewed-by: Christian Fremerey <chfremer@chromium.org>
Commit-Queue: Matthew Cary (CET) <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681366}

services/video_capture/test/fake_device_unittest.cc

@@ -151,8 +151,8 @@ TEST_F(FakeVideoCaptureDeviceTest, BuffersGetRetiredWhenDeviceIsStopped) {
   ASSERT_TRUE(known_buffer_ids.empty());
 }
 
-// This requires platforms where base::SharedMemoryHandle is backed by a
-// file descriptor.
+// This requires the linux platform, where shared regions are backed by a file
+// descriptor.
 #if defined(OS_LINUX)
 TEST_F(FakeVideoCaptureDeviceTest,
        ReceiveFramesViaFileDescriptorHandlesForSharedMemory) {