reapply r70628. It was wrongly blamed for breaking Linux valgrind bots.

net/base/capturing_net_log.h

Index: net/base/capturing_net_log.h
diff --git a/net/base/capturing_net_log.h b/net/base/capturing_net_log.h
index 9254725b53627b1dbf769f2e867e519a954a4ad0..193d641cf42f6722223bd3511a73fadde2c9c6e8 100644
--- a/net/base/capturing_net_log.h
+++ b/net/base/capturing_net_log.h
@@ -61,6 +61,8 @@ class CapturingNetLog : public NetLog {
 
   void Clear();
 
+  void SetLogLevel(NetLog::LogLevel log_level);
+
  private:
   // Needs to be "mutable" so can use it in GetEntries().
   mutable Lock lock_;
@@ -71,6 +73,8 @@ class CapturingNetLog : public NetLog {
   size_t max_num_entries_;
   EntryList entries_;
 
+  NetLog::LogLevel log_level_;
+
   DISALLOW_COPY_AND_ASSIGN(CapturingNetLog);
 };
 
@@ -97,6 +101,9 @@ class CapturingBoundNetLog {
 
   void Clear();
 
+  // Sets the log level of the underlying CapturingNetLog.
+  void SetLogLevel(NetLog::LogLevel log_level);
+
  private:
   NetLog::Source source_;
   scoped_ptr<CapturingNetLog> capturing_net_log_;