Cleanup the OkHttpStreamFetcher class.

Updates to OkHttp 3.9.1 and removes the work around made redundant by
the new version.

Removes some unnecessary accessor class avoidance. 

Clarifies why call is volatile and the rest of the variables are not.

Fixes #2355.

gradle.properties

@@ -17,7 +17,7 @@ POM_DEVELOPER_NAME=Sam Judd
 POM_DEVELOPER_EMAIL=[email protected]
 ANDROID_SUPPORT_VERSION=27.0.2
 VOLLEY_VERSION=1.0.0
-OK_HTTP_VERSION=3.9.0
+OK_HTTP_VERSION=3.9.1
 ANDROID_GRADLE_VERSION=3.0.1
 DAGGER_VERSION=2.11
 

integration/okhttp3/src/main/java/com/bumptech/glide/integration/okhttp3/OkHttpStreamFetcher.java

@@ -1,6 +1,5 @@
 package com.bumptech.glide.integration.okhttp3;
 
-import android.os.Build;
 import android.support.annotation.NonNull;
 import android.util.Log;
 import com.bumptech.glide.Priority;
@@ -10,7 +9,6 @@
 import com.bumptech.glide.load.model.GlideUrl;
 import com.bumptech.glide.util.ContentLengthInputStream;
 import com.bumptech.glide.util.Preconditions;
-import com.bumptech.glide.util.Synthetic;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Map;
@@ -26,10 +24,12 @@ public class OkHttpStreamFetcher implements DataFetcher<InputStream>, okhttp3.Ca
   private static final String TAG = "OkHttpFetcher";
   private final Call.Factory client;
   private final GlideUrl url;
-  @SuppressWarnings("WeakerAccess") @Synthetic InputStream stream;
-  @SuppressWarnings("WeakerAccess") @Synthetic ResponseBody responseBody;
-  private volatile Call call;
+  private InputStream stream;
+  private ResponseBody responseBody;
   private DataCallback<? super InputStream> callback;
+  // call may be accessed on the main thread while the object is in use on other threads. All other
+  // accesses to variables may occur on different threads, but only one at a time.
+  private volatile Call call;
 
   // Public API.
   @SuppressWarnings("WeakerAccess")
@@ -50,21 +50,7 @@ public void loadData(@NonNull Priority priority,
     this.callback = callback;
 
     call = client.newCall(request);
-    if (Build.VERSION.SDK_INT != Build.VERSION_CODES.O) {
-      call.enqueue(this);
-    } else {
-      try {
-        // Calling execute instead of enqueue is a workaround for #2355, where okhttp throws a
-        // ClassCastException on O.
-        onResponse(call, call.execute());
-      } catch (IOException e) {
-        onFailure(call, e);
-      } catch (ClassCastException e) {
-        // It's not clear that this catch is necessary, the error may only occur even on O if
-        // enqueue is used.
-        onFailure(call, new IOException("Workaround for framework bug on O", e));
-      }
-    }
+    call.enqueue(this);
   }
 
   @Override