[trivial] Event sink default should match root logger level

Problem

EventSink defaults to capturing the root logger at Level.ALL.  This is
problematic because some log messages are computed lazily, and it would
be too easy to unwittingly force these messages with EventSink's
defaults.

Solution

Match the log level of the root logger. This is what service owners
would set to a reasonable default.

RB_ID=639266

util-logging/src/main/scala/com/twitter/logging/Logger.scala

@@ -42,6 +42,16 @@ object Level {
   private[logging] val AllLevels: Seq[Level] =
     Seq(OFF, FATAL, CRITICAL, ERROR, WARNING, INFO, DEBUG, TRACE, ALL)
 
+  /**
+   * Associate [[java.util.logging.Level]] and `Level` by their integer
+   * values. If there is no match, we return `None`.
+   */
+  def fromJava(level: javalog.Level): Option[Level] =
+    AllLevels.find(_.value == level.intValue)
+
+  /**
+   * Get a `Level` by its name, or `None` if there is no match.
+   */
   def parse(name: String): Option[Level] = AllLevels.find(_.name == name)
 }
 

util-logging/src/test/scala/com/twitter/logging/LoggerTest.scala

@@ -401,6 +401,24 @@ class LoggerTest extends WordSpec with TempFolder with BeforeAndAfter {
     }
   }
 
+  "Levels.fromJava" should {
+    "return a corresponding level if it exists" in {
+      assert(Level.fromJava(javalog.Level.OFF) == Some(Level.OFF))
+      assert(Level.fromJava(javalog.Level.SEVERE) == Some(Level.FATAL))
+      // No corresponding level for ERROR and CRITICAL in javalog.
+      assert(Level.fromJava(javalog.Level.WARNING) == Some(Level.WARNING))
+      assert(Level.fromJava(javalog.Level.INFO) == Some(Level.INFO))
+      assert(Level.fromJava(javalog.Level.FINE) == Some(Level.DEBUG))
+      assert(Level.fromJava(javalog.Level.FINER) == Some(Level.TRACE))
+      assert(Level.fromJava(javalog.Level.ALL) == Some(Level.ALL))
+    }
+
+    "return None for non corresponding levels" in {
+      assert(Level.fromJava(javalog.Level.CONFIG) == None)
+      assert(Level.fromJava(javalog.Level.FINEST) == None)
+    }
+  }
+
   "Levels.parse" should {
     "return Levels for valid names" in {
       assert(Level.parse("INFO") == Some(Level.INFO))