Reland "Injectable logging"

Any injected loggable or NativeLogger would be deleted if PCFactory
was reinitialized without calling setInjectableLogger. Now native
logging is not implemented as a Loggable, so it will remain active
unless a Loggable is injected.

This is a reland of 59216ec4a4151b1ba5478c8f2b5c9f01f4683d7f

Original change's description:
> Injectable logging
>
> Allows passing a Loggable to PCFactory.initializationOptions, which
> is then injected to Logging.java and logging.h. Future log messages
> in both Java and native will then be passed to this Loggable.
>
> Bug: webrtc:9225
> Change-Id: I2ff693380639448301a78a93dc11d3a0106f0967
> Reviewed-on: https://webrtc-review.googlesource.com/73243
> Commit-Queue: Paulina Hensman <phensman@webrtc.org>
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#23241}

Bug: webrtc:9225
Change-Id: I2fe3fbc8c323814284bb62e43fe1870bdab581ee
TBR: kwiberg
Reviewed-on: https://webrtc-review.googlesource.com/77140
Commit-Queue: Paulina Hensman <phensman@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23310}

rtc_base/java/src/org/webrtc/Logging.java

@@ -15,21 +15,35 @@ import java.io.StringWriter;
 import java.util.EnumSet;
 import java.util.logging.Level;
 import java.util.logging.Logger;
+import javax.annotation.Nullable;
+import org.webrtc.Loggable;
 
 /**
- * Java wrapper for WebRTC logging. Logging defaults to java.util.logging.Logger, but will switch to
- * native logging (rtc::LogMessage) if one of the following static functions are called from the
- * app:
+ * Java wrapper for WebRTC logging. Logging defaults to java.util.logging.Logger, but a custom
+ * logger implementing the Loggable interface can be injected along with a Severity. All subsequent
+ * log messages will then be redirected to the injected Loggable, except those with a severity lower
+ * than the specified severity, which will be discarded.
+ *
+ * It is also possible to switch to native logging (rtc::LogMessage) if one of the following static
+ * functions are called from the app:
  * - Logging.enableLogThreads
  * - Logging.enableLogTimeStamps
  * - Logging.enableLogToDebugOutput
  *
- * Using these APIs requires that the native library is loaded, using
- * PeerConnectionFactory.initialize.
+ * The priority goes:
+ * 1. Injected loggable
+ * 2. Native logging
+ * 3. Fallback logging.
+ * Only one method will be used at a time.
+ *
+ * Injecting a Loggable or using any of the enable... methods requires that the native library is
+ * loaded, using PeerConnectionFactory.initialize.
  */
 public class Logging {
   private static final Logger fallbackLogger = createFallbackLogger();
   private static volatile boolean loggingEnabled;
+  @Nullable private static Loggable loggable;
+  private static Severity loggableSeverity;
 
   private static Logger createFallbackLogger() {
     final Logger fallbackLogger = Logger.getLogger("org.webrtc.Logging");
@@ -37,6 +51,17 @@ public class Logging {
     return fallbackLogger;
   }
 
+  static void injectLoggable(Loggable injectedLoggable, Severity severity) {
+    if (injectedLoggable != null) {
+      loggable = injectedLoggable;
+      loggableSeverity = severity;
+    }
+  }
+
+  static void deleteInjectedLoggable() {
+    loggable = null;
+  }
+
   // TODO(solenberg): Remove once dependent projects updated.
   @Deprecated
   public enum TraceLevel {
@@ -83,11 +108,26 @@ public class Logging {
   // TODO(bugs.webrtc.org/8491): Remove NoSynchronizedMethodCheck suppression.
   @SuppressWarnings("NoSynchronizedMethodCheck")
   public static synchronized void enableLogToDebugOutput(Severity severity) {
+    if (loggable != null) {
+      throw new IllegalStateException(
+          "Logging to native debug output not supported while Loggable is injected. "
+          + "Delete the Loggable before calling this method.");
+    }
     nativeEnableLogToDebugOutput(severity.ordinal());
     loggingEnabled = true;
   }
 
   public static void log(Severity severity, String tag, String message) {
+    if (loggable != null) {
+      // Filter log messages below loggableSeverity.
+      if (severity.ordinal() < loggableSeverity.ordinal()) {
+        return;
+      }
+      loggable.onLogMessage(message, severity, tag);
+      return;
+    }
+
+    // Try native logging if no loggable is injected.
     if (loggingEnabled) {
       nativeLog(severity.ordinal(), tag, message);
       return;