diff -r 000000000000 -r 6474c204b198 mobile/android/base/background/common/log/writers/AndroidLevelCachingLogWriter.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/background/common/log/writers/AndroidLevelCachingLogWriter.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,126 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.background.common.log.writers;
+
+import java.util.IdentityHashMap;
+import java.util.Map;
+
+import android.util.Log;
+
+/**
+ * Make a <code>LogWriter</code> only log when the Android log system says to.
+ */
+public class AndroidLevelCachingLogWriter extends LogWriter {
+  protected final LogWriter inner;
+
+  public AndroidLevelCachingLogWriter(LogWriter inner) {
+    this.inner = inner;
+  }
+
+  // I can't believe we have to implement this ourselves.
+  // These aren't synchronized (and neither are the setters) because
+  // the logging calls themselves are synchronized.
+  private Map<String, Boolean> isErrorLoggable   = new IdentityHashMap<String, Boolean>();
+  private Map<String, Boolean> isWarnLoggable    = new IdentityHashMap<String, Boolean>();
+  private Map<String, Boolean> isInfoLoggable    = new IdentityHashMap<String, Boolean>();
+  private Map<String, Boolean> isDebugLoggable   = new IdentityHashMap<String, Boolean>();
+  private Map<String, Boolean> isVerboseLoggable = new IdentityHashMap<String, Boolean>();
+
+  /**
+   * Empty the caches of log levels.
+   */
+  public void refreshLogLevels() {
+    isErrorLoggable   = new IdentityHashMap<String, Boolean>();
+    isWarnLoggable    = new IdentityHashMap<String, Boolean>();
+    isInfoLoggable    = new IdentityHashMap<String, Boolean>();
+    isDebugLoggable   = new IdentityHashMap<String, Boolean>();
+    isVerboseLoggable = new IdentityHashMap<String, Boolean>();
+  }
+
+  private boolean shouldLogError(String logTag) {
+    Boolean out = isErrorLoggable.get(logTag);
+    if (out != null) {
+      return out.booleanValue();
+    }
+    out = Log.isLoggable(logTag, Log.ERROR);
+    isErrorLoggable.put(logTag, out);
+    return out;
+  }
+
+  private boolean shouldLogWarn(String logTag) {
+    Boolean out = isWarnLoggable.get(logTag);
+    if (out != null) {
+      return out.booleanValue();
+    }
+    out = Log.isLoggable(logTag, Log.WARN);
+    isWarnLoggable.put(logTag, out);
+    return out;
+  }
+
+  private boolean shouldLogInfo(String logTag) {
+    Boolean out = isInfoLoggable.get(logTag);
+    if (out != null) {
+      return out.booleanValue();
+    }
+    out = Log.isLoggable(logTag, Log.INFO);
+    isInfoLoggable.put(logTag, out);
+    return out;
+  }
+
+  private boolean shouldLogDebug(String logTag) {
+    Boolean out = isDebugLoggable.get(logTag);
+    if (out != null) {
+      return out.booleanValue();
+    }
+    out = Log.isLoggable(logTag, Log.DEBUG);
+    isDebugLoggable.put(logTag, out);
+    return out;
+  }
+
+  @Override
+  public boolean shouldLogVerbose(String logTag) {
+    Boolean out = isVerboseLoggable.get(logTag);
+    if (out != null) {
+      return out.booleanValue();
+    }
+    out = Log.isLoggable(logTag, Log.VERBOSE);
+    isVerboseLoggable.put(logTag, out);
+    return out;
+  }
+
+  public void error(String tag, String message, Throwable error) {
+    if (shouldLogError(tag)) {
+      inner.error(tag, message, error);
+    }
+  }
+
+  public void warn(String tag, String message, Throwable error) {
+    if (shouldLogWarn(tag)) {
+      inner.warn(tag, message, error);
+    }
+  }
+
+  public void info(String tag, String message, Throwable error) {
+    if (shouldLogInfo(tag)) {
+      inner.info(tag, message, error);
+    }
+  }
+
+  public void debug(String tag, String message, Throwable error) {
+    if (shouldLogDebug(tag)) {
+      inner.debug(tag, message, error);
+    }
+  }
+
+  public void trace(String tag, String message, Throwable error) {
+    if (shouldLogVerbose(tag)) {
+      inner.trace(tag, message, error);
+    }
+  }
+
+  public void close() {
+    inner.close();
+  }
+}