title: Android App integration with Firestore: Could not reach firestore backend
body: <p>I am having trouble fetching data from firestore on android app.</p>
  
  <p>Just for testing, I was trying to get data as follows:-</p>
  
  <pre><code>FirebaseFirestore db = FirebaseFirestore.getInstance();
          this.collectionReference = db.collection("userData/tracking/users/someuser/books");
          db.document("userData/tracking").get().addOnSuccessListener(new OnSuccessListener&lt;DocumentSnapshot&gt;() {
              @Override
              public void onSuccess(DocumentSnapshot documentSnapshot) {
                  if (documentPath.isEmpty())
                  {
                      //some code....
                  }
              }
          });
  
  Note: userData/tracking/**users/someuser/books** part in bold doesn't exists. 
  userData/tracking document exists.
  
  But running the android app on debug mode, I get the following errors on console:-
  W/common.FileUtils: Failed to set dir world executable: java.io.FileNotFoundException: /data/user_de/0/com.google.android.gms/files/gmscore_global_dirs.txt: open failed: EACCES (Permission denied)
  W/System: ClassLoader referenced unknown path: /system/priv-app/PrebuiltGmsCore/lib/x86
  W/common.FileUtils: Failed to set dir world executable: java.io.FileNotFoundException: /data/user_de/0/com.google.android.gms/files/gmscore_global_dirs.txt: open failed: EACCES (Permission denied)
  W/System: ClassLoader referenced unknown path: /system/priv-app/PrebuiltGmsCore/lib/x86
  W/common.FileUtils: Failed to set dir world executable: java.io.FileNotFoundException: /data/user_de/0/com.google.android.gms/files/gmscore_global_dirs.txt: open failed: EACCES (Permission denied)
  W/System: ClassLoader referenced unknown path: /system/priv-app/PrebuiltGmsCore/lib/x86
  W/common.FileUtils: Failed to set dir world executable: java.io.FileNotFoundException: /data/user_de/0/com.google.android.gms/files/gmscore_global_dirs.txt: open failed: EACCES (Permission denied)
  W/System: ClassLoader referenced unknown path: /system/priv-app/PrebuiltGmsCore/lib/x86
  W/linker: /data/user_de/0/com.google.android.gms/app_extracted_libs/x86/libconscrypt_gmscore_jni.so: unused DT entry: type 0xf arg 0x91
  V/NativeCrypto: Registering com/google/android/gms/org/conscrypt/NativeCrypto's 279 native methods...
  I/art: Background sticky concurrent mark sweep GC freed 20733(1775KB) AllocSpace objects, 34(680KB) LOS objects, 6% free, 34MB/37MB, paused 12.506ms total 132.706ms
  I/ProviderInstaller: Installed default security provider GmsCore_OpenSSL
  W/Firestore: (0.6.6-dev) [OnlineStateTracker]: Could not reach Firestore backend.
  </code></pre>
  
  <p>Pardon me for any silly mistakes as I am using <code>Firestore</code> for the first time. Surely, I am missing something trivial. Any help or suggestions will be great!</p>