Save recent Widevine CDM logs

Bug: 162255728
Test: cdm unit tests
Change-Id: Ibc0daf374bedd8ac2a9a0515835e2775045962a7

libwvdrmengine/cdm/util/include/log.h

@@ -7,6 +7,11 @@
 #ifndef WVCDM_UTIL_LOG_H_
 #define WVCDM_UTIL_LOG_H_
 
+#include <cstdint>
+#include <deque>
+#include <mutex>
+#include <string>
+#include <vector>
 #include "util_common.h"
 
 namespace wvcdm {
@@ -27,6 +32,24 @@ typedef enum {
 
 extern LogPriority g_cutoff;
 
+struct LogMessage {
+  int64_t time_ms_;
+  LogPriority priority_;
+  std::string message_;
+};
+
+class LogBuffer {
+ public:
+  static const int MAX_CAPACITY = 100;
+  void addLog(const LogMessage& log);
+  std::vector<LogMessage> getLogs();
+ private:
+  std::deque<LogMessage> buffer_;
+  std::mutex mutex_;
+};
+
+extern LogBuffer g_logbuf;
+
 // Enable/disable verbose logging (LOGV).
 // This function is supplied for cases where the system layer does not
 // initialize logging.  This is also needed to initialize logging in