Access UpdateManager via getInstance().

This API changes in AT O.

Bug: internal b/77915277
Test: Compile
Change-Id: Id3c651378d9ac12319cd5aa437e9c56d48ea3096
Reviewed-on: https://chromium-review.googlesource.com/1033472
Commit-Queue: Doug Horn <doughorn@google.com>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558312}

chromecast/browser/android/apk/src/org/chromium/chromecast/shell/CastSysInfoAndroidThings.java

@@ -14,10 +14,8 @@ import org.chromium.base.annotations.JNINamespace;
  */
 @JNINamespace("chromecast")
 public final class CastSysInfoAndroidThings {
-    private static final UpdateManager sUpdateManager = new UpdateManager();
-
     @CalledByNative
     private static String getReleaseChannel() {
-        return sUpdateManager.getChannel();
+        return UpdateManager.getInstance().getChannel();
     }
 }