Allow a direct executor for Cronet's response handling thread.

We want to experiment with a direct executor to avoid thread hops between the
network thread and the response handling thread. This change is needed to do
so.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161812382

extensions/cronet/src/androidTest/java/com/google/android/exoplayer2/ext/cronet/CronetDataSourceTest.java

@@ -124,6 +124,7 @@ public final class CronetDataSourceTest {
     when(mockCronetEngine.newUrlRequestBuilder(
     when(mockCronetEngine.newUrlRequestBuilder(
             anyString(), any(UrlRequest.Callback.class), any(Executor.class)))
             anyString(), any(UrlRequest.Callback.class), any(Executor.class)))
         .thenReturn(mockUrlRequestBuilder);
         .thenReturn(mockUrlRequestBuilder);
+    when(mockUrlRequestBuilder.allowDirectExecutor()).thenReturn(mockUrlRequestBuilder);
     when(mockUrlRequestBuilder.build()).thenReturn(mockUrlRequest);
     when(mockUrlRequestBuilder.build()).thenReturn(mockUrlRequest);
     mockStatusResponse();
     mockStatusResponse();
 
 
@@ -683,6 +684,15 @@ public final class CronetDataSourceTest {
     }
     }
   }
   }
 
 
+  @Test
+  public void testAllowDirectExecutor() throws HttpDataSourceException {
+    testDataSpec = new DataSpec(Uri.parse(TEST_URL), 1000, 5000, null);
+    mockResponseStartSuccess();
+
+    dataSourceUnderTest.open(testDataSpec);
+    verify(mockUrlRequestBuilder).allowDirectExecutor();
+  }
+
   // Helper methods.
   // Helper methods.
 
 
   private void mockStatusResponse() {
   private void mockStatusResponse() {

extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/CronetDataSource.java

@@ -127,7 +127,11 @@ public class CronetDataSource extends UrlRequest.Callback implements HttpDataSou
 
 
   /**
   /**
    * @param cronetEngine A CronetEngine.
    * @param cronetEngine A CronetEngine.
-   * @param executor The {@link java.util.concurrent.Executor} that will perform the requests.
+   * @param executor The {@link java.util.concurrent.Executor} that will handle responses.
+   *     This may be a direct executor (i.e. executes tasks on the calling thread) in order
+   *     to avoid a thread hop from Cronet's internal network thread to the response handling
+   *     thread. However, to avoid slowing down overall network performance, care must be taken
+   *     to make sure response handling is a fast operation when using a direct executor.
    * @param contentTypePredicate An optional {@link Predicate}. If a content type is rejected by the
    * @param contentTypePredicate An optional {@link Predicate}. If a content type is rejected by the
    *     predicate then an {@link InvalidContentTypeException} is thrown from
    *     predicate then an {@link InvalidContentTypeException} is thrown from
    *     {@link #open(DataSpec)}.
    *     {@link #open(DataSpec)}.
@@ -141,7 +145,11 @@ public class CronetDataSource extends UrlRequest.Callback implements HttpDataSou
 
 
   /**
   /**
    * @param cronetEngine A CronetEngine.
    * @param cronetEngine A CronetEngine.
-   * @param executor The {@link java.util.concurrent.Executor} that will perform the requests.
+   * @param executor The {@link java.util.concurrent.Executor} that will handle responses.
+   *     This may be a direct executor (i.e. executes tasks on the calling thread) in order
+   *     to avoid a thread hop from Cronet's internal network thread to the response handling
+   *     thread. However, to avoid slowing down overall network performance, care must be taken
+   *     to make sure response handling is a fast operation when using a direct executor.
    * @param contentTypePredicate An optional {@link Predicate}. If a content type is rejected by the
    * @param contentTypePredicate An optional {@link Predicate}. If a content type is rejected by the
    *     predicate then an {@link InvalidContentTypeException} is thrown from
    *     predicate then an {@link InvalidContentTypeException} is thrown from
    *     {@link #open(DataSpec)}.
    *     {@link #open(DataSpec)}.
@@ -416,8 +424,8 @@ public class CronetDataSource extends UrlRequest.Callback implements HttpDataSou
   // Internal methods.
   // Internal methods.
 
 
   private UrlRequest buildRequest(DataSpec dataSpec) throws OpenException {
   private UrlRequest buildRequest(DataSpec dataSpec) throws OpenException {
-    UrlRequest.Builder requestBuilder = cronetEngine.newUrlRequestBuilder(dataSpec.uri.toString(),
-        this, executor);
+    UrlRequest.Builder requestBuilder = cronetEngine.newUrlRequestBuilder(
+        dataSpec.uri.toString(), this, executor).allowDirectExecutor();
     // Set the headers.
     // Set the headers.
     boolean isContentTypeHeaderSet = false;
     boolean isContentTypeHeaderSet = false;
     if (defaultRequestProperties != null) {
     if (defaultRequestProperties != null) {