Replace uses of hash_map in //base

base/trace_event/trace_log.cc

Index: base/trace_event/trace_log.cc
diff --git a/base/trace_event/trace_log.cc b/base/trace_event/trace_log.cc
index 3e9375db53efee7d453e93f55448a15ca285cd4c..5cdf53539231e22a877c1933f96f3a42e28b4152 100644
--- a/base/trace_event/trace_log.cc
+++ b/base/trace_event/trace_log.cc
@@ -1229,8 +1229,7 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
 
       AutoLock thread_info_lock(thread_info_lock_);
 
-      hash_map<int, std::string>::iterator existing_name =
-          thread_names_.find(thread_id);
+      auto existing_name = thread_names_.find(thread_id);
       if (existing_name == thread_names_.end()) {
         // This is a new thread id, and a new name.
         thread_names_[thread_id] = new_name;