Use angle::FlatUnorderedMap as storage for AttributMap AttributeMap was using std::map which allocates storage from heap it is not ideal for small map like attribute map. So replace it with angle::FlatUnorderedMap with 2 default size (Chromium creates a lot of gl fence with 2 attributes on Android). Bug: chromium:1336126 Change-Id: I129fe603df2fd475ae1b0e35b63d4d0171bbae09 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3812565 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>