Fix launcher scroll distance for TAPL tests.

Test is passing correctly but for the wrong reasons. If we attempted to use a different distance it would have failed.

Bug: 197630182
Test: manual
Change-Id: Ib275b89c86cdb9f75d40b9d25c8c498098b543b7

src/com/android/launcher3/testing/TestProtocol.java

@@ -108,6 +108,7 @@ public final class TestProtocol {
             "get-focused-task-height-for-tablet";
     public static final String REQUEST_GET_GRID_TASK_SIZE_RECT_FOR_TABLET =
             "get-grid-task-size-rect-for-tablet";
+    public static final String REQUEST_GET_OVERVIEW_PAGE_SPACING = "get-overview-page-spacing";
     public static final String REQUEST_ENABLE_ROTATION = "enable_rotation";
 
     public static Long sForcePauseTimeout;