adb: fix `push --sync` with multiple inputs.

Previously, when push --sync was used with multiple files, we tried to
stat a remote file with pending acknowledgements still in the socket
buffer, which leads to an abort when we read ID_OKAY instead of the
response we were expecting.

This patch changes the behavior to always wait for acknowledgements if
we're pushing with --sync (or `adb sync`). This results in a ~100ms
regression during a 10 second sync of every file on the system image,
but that's not very much, so perhaps we should consider doing this
always.

Bug: http://b/166155032
Test: test_device.py
Change-Id: I7110243071ba5fbaa77dcc76f42a19d9ed2b4195

adb/client/file_sync_client.cpp

@@ -1053,7 +1053,7 @@ static bool sync_send(SyncConnection& sc, const std::string& lpath, const std::s
         if (!sc.SendSmallFile(rpath, mode, lpath, rpath, mtime, buf, data_length, dry_run)) {
             return false;
         }
-        return sc.ReadAcknowledgements();
+        return sc.ReadAcknowledgements(sync);
 #endif
     }
 
@@ -1077,7 +1077,7 @@ static bool sync_send(SyncConnection& sc, const std::string& lpath, const std::s
             return false;
         }
     }
-    return sc.ReadAcknowledgements();
+    return sc.ReadAcknowledgements(sync);
 }
 
 static bool sync_recv_v1(SyncConnection& sc, const char* rpath, const char* lpath, const char* name,

adb/test_device.py

@@ -1271,6 +1271,31 @@ class FileOperationsTest:
                 if temp_dir is not None:
                     shutil.rmtree(temp_dir)
 
+        def test_push_sync_multiple(self):
+            """Sync multiple host directories to a specific path."""
+
+            try:
+                temp_dir = tempfile.mkdtemp()
+                temp_files = make_random_host_files(in_dir=temp_dir, num_files=32)
+
+                device_dir = posixpath.join(self.DEVICE_TEMP_DIR, 'sync_src_dst')
+
+                # Clean up any stale files on the device.
+                device = adb.get_device()  # pylint: disable=no-member
+                device.shell(['rm', '-rf', device_dir])
+                device.shell(['mkdir', '-p', device_dir])
+
+                host_paths = [os.path.join(temp_dir, x.base_name) for x in temp_files]
+                device.push(host_paths, device_dir, sync=True)
+
+                self.verify_sync(device, temp_files, device_dir)
+
+                self.device.shell(['rm', '-rf', self.DEVICE_TEMP_DIR])
+            finally:
+                if temp_dir is not None:
+                    shutil.rmtree(temp_dir)
+
+
         def test_push_dry_run_nonexistent_file(self):
             """Push with dry run."""