Factor out authorization from AudioRendererHost.

content/public/browser/media_device_id.cc

Index: content/public/browser/media_device_id.cc
diff --git a/content/public/browser/media_device_id.cc b/content/public/browser/media_device_id.cc
index 97faa1e1a40ec9476959b9458e1d1e4345c98909..e7a3ac970274857163f759239bea0cc6d5b2a677 100644
--- a/content/public/browser/media_device_id.cc
+++ b/content/public/browser/media_device_id.cc
@@ -3,8 +3,10 @@
 // found in the LICENSE file.
 #include "content/public/browser/media_device_id.h"
 
+#include "base/strings/string_util.h"
 #include "content/browser/browser_main_loop.h"
 #include "content/browser/renderer_host/media/media_stream_manager.h"
+#include "media/audio/audio_device_description.h"
 
 namespace content {
 
@@ -36,4 +38,18 @@ bool GetMediaDeviceIDForHMAC(MediaStreamType stream_type,
       device_id);
 }
 
+bool IsValidDeviceId(const std::string& device_id) {
+  constexpr int hash_size = 64;  // 32 bytes * 2 char/byte hex encoding
+  if (media::AudioDeviceDescription::IsDefaultDevice(device_id) ||
+      device_id == media::AudioDeviceDescription::kCommunicationsDeviceId)
+    return true;
+
+  if (device_id.length() != hash_size)
+    return false;
+
+  return std::all_of(device_id.cbegin(), device_id.cend(), [](const char& c) {
+    return base::IsAsciiLower(c) || base::IsAsciiDigit(c);
+  });
+}
+
 }  // namespace content