content: Use stl utilities from the base namespace

The utilities in base/stl_util.h have been moved from the global
into the base namespace. This patch updates the call sites accordingly.

No functional changes.

BUG=636301
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2228403003
Cr-Commit-Position: refs/heads/master@{#411614}
diff --git a/content/browser/plugin_private_storage_helper.cc b/content/browser/plugin_private_storage_helper.cc
index d7c6228a..3d241ea 100644
--- a/content/browser/plugin_private_storage_helper.cc
+++ b/content/browser/plugin_private_storage_helper.cc
@@ -395,7 +395,7 @@
   // If a specific origin is provided, then check that it is in the list
   // returned and remove all the other origins.
   if (!storage_origin.is_empty()) {
-    if (!ContainsKey(origins, storage_origin)) {
+    if (!base::ContainsKey(origins, storage_origin)) {
       // Nothing matches, so nothing to do.
       callback.Run();
       return;