[Impeller] Fix vertex counts in some display list tests (#51111)

impeller/display_list/dl_unittests.cc

diff --git a/impeller/display_list/dl_unittests.cc b/impeller/display_list/dl_unittests.cc
index 6b6f8a1..5da4606 100644
--- a/impeller/display_list/dl_unittests.cc
+++ b/impeller/display_list/dl_unittests.cc
@@ -1520,8 +1520,9 @@
   std::vector<uint16_t> indices = {0, 1, 2, 0, 2, 3};
 
   auto vertices = flutter::DlVertices::Make(
-      flutter::DlVertexMode::kTriangles, 6, positions.data(),
-      /*texture_coordinates=*/nullptr, /*colors=*/nullptr, 6, indices.data());
+      flutter::DlVertexMode::kTriangles, positions.size(), positions.data(),
+      /*texture_coordinates=*/nullptr, /*colors=*/nullptr, indices.size(),
+      indices.data());
 
   flutter::DisplayListBuilder builder;
   flutter::DlPaint paint;
@@ -1541,8 +1542,9 @@
   std::vector<flutter::DlColor> colors = {color, color, color, color};
 
   auto vertices = flutter::DlVertices::Make(
-      flutter::DlVertexMode::kTriangles, 6, positions.data(),
-      /*texture_coordinates=*/nullptr, colors.data(), 6, indices.data());
+      flutter::DlVertexMode::kTriangles, positions.size(), positions.data(),
+      /*texture_coordinates=*/nullptr, colors.data(), indices.size(),
+      indices.data());
 
   flutter::DisplayListBuilder builder;
   flutter::DlPaint paint;