viz: Use child sequence number from parent if embed token changes

If the first LocalSurfaceId provided by the parent has a child sequence
number greater than 1, we should use that number. This is a speculative
fix for https://crbug.com/1051625

Bug: 1051625,1043109
Change-Id: I8b5fb86d42aa6e087e64c9e86a1de703e0b74723
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2092417
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749370}

components/viz/common/surfaces/child_local_surface_id_allocator.cc

@@ -72,10 +72,13 @@ bool ChildLocalSurfaceIdAllocator::UpdateFromParent(
         parent_local_surface_id_allocation.allocation_time();
   }
 
+  // If embed token has changed, accept all fields from the parent
+  // including child sequence number.
   if (current_local_surface_id.embed_token() !=
       parent_allocated_local_surface_id.embed_token()) {
     current_local_surface_id_allocation_.local_surface_id_
-        .child_sequence_number_ = 1;
+        .child_sequence_number_ =
+        parent_allocated_local_surface_id.child_sequence_number_;
   }
 
   current_local_surface_id_allocation_.local_surface_id_