Wait for DataTransport callback task at crash time

Improves reliability of sending crash reports at crash time in the
case that the process would exit before Crashlytics has received
the asynchronous callback from DataTransport.

Author: mrwillis21

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/CrashlyticsController.java

@@ -435,9 +435,10 @@ public Task<Void> then(@Nullable AppSettingsData appSettingsData)
                             // Data collection is enabled, so it's safe to send the report.
                             boolean dataCollectionToken = true;
                             sendSessionReports(appSettingsData, dataCollectionToken);
-                            reportingCoordinator.sendReports(
-                                executor, DataTransportState.getState(appSettingsData));
-                            return recordFatalFirebaseEventTask;
+                            return Tasks.whenAll(
+                                reportingCoordinator.sendReports(
+                                    executor, DataTransportState.getState(appSettingsData)),
+                                recordFatalFirebaseEventTask);
                           }
                         });
               }

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/SessionReportingCoordinator.java

@@ -18,6 +18,7 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import com.google.android.gms.tasks.Task;
+import com.google.android.gms.tasks.Tasks;
 import com.google.firebase.crashlytics.internal.Logger;
 import com.google.firebase.crashlytics.internal.log.LogFileManager;
 import com.google.firebase.crashlytics.internal.model.CrashlyticsReport;
@@ -170,16 +171,17 @@ public void removeAllReports() {
    *     sent.
    * @param dataTransportState used to determine whether to send the report before cleaning it up.
    */
-  public void sendReports(
+  Task<Void> sendReports(
       @NonNull Executor reportSendCompleteExecutor,
       @NonNull DataTransportState dataTransportState) {
     if (dataTransportState == DataTransportState.NONE) {
       Logger.getLogger().d("Send via DataTransport disabled. Removing DataTransport reports.");
       reportPersistence.deleteAllReports();
-      return;
+      return Tasks.forResult(null);
     }
     final List<CrashlyticsReportWithSessionId> reportsToSend =
         reportPersistence.loadFinalizedReports();
+    final List<Task<Boolean>> sendTasks = new ArrayList<>();
     for (CrashlyticsReportWithSessionId reportToSend : reportsToSend) {
       if (reportToSend.getReport().getType() == CrashlyticsReport.Type.NATIVE
           && dataTransportState != DataTransportState.ALL) {
@@ -189,10 +191,12 @@ public void sendReports(
         continue;
       }
 
-      reportsSender
-          .sendReport(reportToSend)
-          .continueWith(reportSendCompleteExecutor, this::onReportSendComplete);
+      sendTasks.add(
+          reportsSender
+              .sendReport(reportToSend)
+              .continueWith(reportSendCompleteExecutor, this::onReportSendComplete));
     }
+    return Tasks.whenAll(sendTasks);
   }
 
   private void persistEvent(