Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I8c5e5b0ceb4fa8fc511d15d58966d241ca8f8671

webservd/binder_server.cc

diff --git a/webservd/binder_server.cc b/webservd/binder_server.cc
index 1fce0a0..bc588cb 100644
--- a/webservd/binder_server.cc
+++ b/webservd/binder_server.cc
@@ -59,7 +59,7 @@
 
 class BinderRequestHandler : public RequestHandlerInterface {
  public:
-  BinderRequestHandler(const sp<IRequestHandler>& handler)
+  explicit BinderRequestHandler(const sp<IRequestHandler>& handler)
       : handler_(handler) {}
 
   void HandleRequest(Request* request) override {