Add functionality to get default media device IDs from user preferences.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 9bbc2e84720ce30fa6b8a34a3f7cf8adc22c6a92..006c2dcc4d606298ebb7bde0da52e00662b03fad 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -2362,6 +2362,12 @@ bool WebContentsImpl::CheckMediaAccessPermission(const GURL& security_origin,
          delegate_->CheckMediaAccessPermission(this, security_origin, type);
 }
 
+std::string WebContentsImpl::GetDefaultMediaDeviceId(MediaStreamType type) {
+  if (!delegate_)
+    return std::string();
+  return delegate_->GetDefaultMediaDeviceId(this, type);
+}
+
 SessionStorageNamespace* WebContentsImpl::GetSessionStorageNamespace(
     SiteInstance* instance) {
   return controller_.GetSessionStorageNamespace(instance);