Realtime Pipeline Integration with SDK + some minor fixes

Author: wu-hui

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/PipelineTest.java

@@ -566,7 +566,7 @@ public void testToUppercase() {
         firestore
             .pipeline()
             .collection(randomCol)
-            .select(field("author").toLower().alias("uppercaseAuthor"))
+            .select(field("author").toUpper().alias("uppercaseAuthor"))
             .limit(1)
             .execute();
     assertThat(waitFor(execute).getResults())

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/QueryToPipelineTest.java

@@ -14,7 +14,6 @@
 
 package com.google.firebase.firestore;
 
-import static com.google.common.io.Files.map;
 import static com.google.firebase.firestore.Filter.and;
 import static com.google.firebase.firestore.Filter.arrayContains;
 import static com.google.firebase.firestore.Filter.arrayContainsAny;

firebase-firestore/src/main/java/com/google/firebase/firestore/Pipeline.kt

@@ -41,7 +41,6 @@ import com.google.firebase.firestore.pipeline.OffsetStage
 import com.google.firebase.firestore.pipeline.Ordering
 import com.google.firebase.firestore.pipeline.PipelineOptions
 import com.google.firebase.firestore.pipeline.RawStage
-import com.google.firebase.firestore.pipeline.RealtimePipelineOptions
 import com.google.firebase.firestore.pipeline.RemoveFieldsStage
 import com.google.firebase.firestore.pipeline.ReplaceStage
 import com.google.firebase.firestore.pipeline.SampleStage
@@ -676,9 +675,10 @@ class PipelineSource internal constructor(private val firestore: FirebaseFiresto
    * pipeline.
    * @return A new [Pipeline] object with [documents].
    */
-  fun documents(vararg documents: String): Pipeline =
+  fun documents(vararg documents: String): Pipeline {
     // Validate document path by converting to DocumentReference
-    documents(*documents.map(firestore::document).toTypedArray())
+    return documents(*documents.map(firestore::document).toTypedArray())
+  }
 
   /**
    * Set the pipeline's source to the documents specified by the given DocumentReferences.
@@ -771,10 +771,6 @@ internal constructor(
 
   private fun append(stage: Stage<*>): RealtimePipeline = with(stages.plus(stage))
 
-  fun execute(): Task<PipelineSnapshot> = execute(null)
-
-  fun execute(options: RealtimePipelineOptions): Task<PipelineSnapshot> = execute(options.options)
-
   fun limit(limit: Int): RealtimePipeline = append(LimitStage(limit))
 
   fun offset(offset: Int): RealtimePipeline = append(OffsetStage(offset))