Misc nit fixes for downloader

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=195358542

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java

@@ -464,13 +464,13 @@ public final class DownloadManager {
     });
   }
 
-  private void logd(String message) {
+  private static void logd(String message) {
     if (DEBUG) {
       Log.d(TAG, message);
     }
   }
 
-  private void logd(String message, Task task) {
+  private static void logd(String message, Task task) {
     logd(message + ": " + task);
   }
 
@@ -710,7 +710,7 @@ public final class DownloadManager {
 
     private void stop() {
       if (changeStateAndNotify(STATE_STARTED, STATE_STARTED_STOPPING)) {
-        downloadManager.logd("Stopping", this);
+        logd("Stopping", this);
         thread.interrupt();
       }
     }
@@ -737,7 +737,7 @@ public final class DownloadManager {
 
     @Override
     public void run() {
-      downloadManager.logd("Task is started", this);
+      logd("Task is started", this);
       Throwable error = null;
       try {
         downloader = action.createDownloader(downloadManager.downloaderConstructorHelper);
@@ -753,15 +753,14 @@ public final class DownloadManager {
             } catch (IOException e) {
               long downloadedBytes = downloader.getDownloadedBytes();
               if (downloadedBytes != errorPosition) {
-                downloadManager.logd(
-                    "Reset error count. downloadedBytes = " + downloadedBytes, this);
+                logd("Reset error count. downloadedBytes = " + downloadedBytes, this);
                 errorPosition = downloadedBytes;
                 errorCount = 0;
               }
               if (currentState != STATE_STARTED || ++errorCount > minRetryCount) {
                 throw e;
               }
-              downloadManager.logd("Download error. Retry " + errorCount, this);
+              logd("Download error. Retry " + errorCount, this);
               Thread.sleep(getRetryDelayMillis(errorCount));
             }
           }

library/core/src/main/java/com/google/android/exoplayer2/offline/ProgressiveDownloader.java

@@ -42,7 +42,7 @@ public final class ProgressiveDownloader implements Downloader {
    * @param uri Uri of the data to be downloaded.
    * @param customCacheKey A custom key that uniquely identifies the original stream. Used for cache
    *     indexing. May be null.
-   * @param constructorHelper a {@link DownloaderConstructorHelper} instance.
+   * @param constructorHelper A {@link DownloaderConstructorHelper} instance.
    */
   public ProgressiveDownloader(
       Uri uri, String customCacheKey, DownloaderConstructorHelper constructorHelper) {

library/core/src/main/java/com/google/android/exoplayer2/offline/SegmentDownloader.java

@@ -75,7 +75,7 @@ public abstract class SegmentDownloader<M extends FilterableManifest<M, K>, K>
 
   /**
    * @param manifestUri The {@link Uri} of the manifest to be downloaded.
-   * @param constructorHelper a {@link DownloaderConstructorHelper} instance.
+   * @param constructorHelper A {@link DownloaderConstructorHelper} instance.
    * @param trackKeys Track keys to select when downloading. If empty, all tracks are downloaded.
    */
   public SegmentDownloader(