Make the logging system static

No initialization is needed anymore and we can use the logging functions
safely at any point of the code (threading is not handled though, so you
might get multiplexed messages if you log from two threads
simultaneously).

platform/android/log_android.cpp

@@ -1,4 +1,4 @@
-#include <mbgl/platform/android/log_android.hpp>
+#include <mbgl/platform/log.hpp>
 
 #define __STDC_FORMAT_MACROS // NDK bug workaround: https://code.google.com/p/android/issues/detail?id=72349
 #include <cinttypes>
@@ -7,7 +7,9 @@
 
 namespace mbgl {
 
-int AndroidLogBackend::severityToPriority(EventSeverity severity) {
+namespace {
+
+int severityToPriority(EventSeverity severity) {
     switch(severity) {
     case EventSeverity::Debug:
         return ANDROID_LOG_DEBUG;
@@ -26,7 +28,9 @@ int AndroidLogBackend::severityToPriority(EventSeverity severity) {
     }
 }
 
-void AndroidLogBackend::record(EventSeverity severity, Event event, int64_t code, const std::string &msg) {
+} // namespace
+
+void Log::platformRecord(EventSeverity severity, Event event, int64_t code, const std::string &msg) {
     __android_log_print(severityToPriority(severity), EventClass(event).c_str(), "(%" PRId64 ") %s", code, msg.c_str());
 }