Add logger specific log level

Previously all logger instances shared the same log level. This commit adds the
ability to specify log level per instance. It also removes the dependence of a
global variable.

Author: haarts

lib/src/filters/debug_filter.dart

@@ -9,7 +9,7 @@ class DebugFilter extends LogFilter {
   bool shouldLog(LogEvent event) {
     var shouldLog = false;
     assert(() {
-      if (event.level.index >= Logger.level.index) {
+      if (event.level.index >= level.index) {
         shouldLog = true;
       }
       return true;

lib/src/filters/production_filter.dart

@@ -4,6 +4,6 @@ part of logger;
 class ProductionFilter extends LogFilter {
   @override
   bool shouldLog(LogEvent event) {
-    return event.level.index >= Logger.level.index;
+    return event.level.index >= level.index;
   }
 }

lib/src/log_filter.dart

@@ -5,6 +5,7 @@ part of logger;
 /// You can implement your own `LogFilter` or use [DebugFilter].
 /// Every implementation should consider [Logger.level].
 abstract class LogFilter {
+  Level level;
   void init() {}
 
   /// Is called every time a new log message is sent and decides if

lib/src/logger.dart

@@ -52,11 +52,16 @@ class Logger {
   /// You can provide a custom [printer], [filter] and [output]. Otherwise the
   /// defaults: [PrettyPrinter], [DebugFilter] and [ConsoleOutput] will be
   /// used.
-  Logger({LogFilter filter, LogPrinter printer, LogOutput output})
-      : _filter = filter ?? DebugFilter(),
+  Logger({
+    LogFilter filter,
+    LogPrinter printer,
+    LogOutput output,
+    Level level,
+  })  : _filter = filter ?? DebugFilter(),
         _printer = printer ?? PrettyPrinter(),
         _output = output ?? ConsoleOutput() {
     _filter.init();
+    _filter.level = level ?? Logger.level;
     _printer._buffer = _outputBuffer;
     _printer.init();
     _output.init();

test/logger_test.dart

@@ -143,4 +143,19 @@ void main() {
     expect(printedError, "Error");
     expect(printedStackTrace, stackTrace);
   });
+
+  test('setting log level above log level of message', () {
+    printedMessage = null;
+    var logger = Logger(
+      filter: ProductionFilter(),
+      printer: callbackPrinter,
+      level: Level.warning,
+    );
+
+    logger.d("This isn't logged");
+    expect(printedMessage, isNull);
+
+    logger.w("This is");
+    expect(printedMessage, "This is");
+  });
 }