Add missing (and remove superfluous) 'explicit' from constructors.

content/common/quota_dispatcher.cc

Index: content/common/quota_dispatcher.cc
diff --git a/content/common/quota_dispatcher.cc b/content/common/quota_dispatcher.cc
index ac45e1d51ee25a3dfb874bb831717e43fdd9c376..4ed2ad033c745267910abc051b273e4a3443e021 100644
--- a/content/common/quota_dispatcher.cc
+++ b/content/common/quota_dispatcher.cc
@@ -24,7 +24,8 @@ namespace {
 // QuotaDispatcher::Callback implementation for WebStorageQuotaCallbacks.
 class WebStorageQuotaDispatcherCallback : public QuotaDispatcher::Callback {
  public:
-  WebStorageQuotaDispatcherCallback(WebKit::WebStorageQuotaCallbacks* callback)
+  explicit WebStorageQuotaDispatcherCallback(
+      WebKit::WebStorageQuotaCallbacks* callback)
       : callbacks_(callback) {
     DCHECK(callbacks_);
   }