perf_tests: Use const definition for inner loop bounds

Change-Id: I1d1bb9ed697c332a315c81c76f8d710927355458
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/178280
Auto-Submit: David Neto <dneto@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/src/dawn/tests/perf_tests/ShaderRobustnessPerf.cpp b/src/dawn/tests/perf_tests/ShaderRobustnessPerf.cpp
index 2b897a2..48d5dde 100644
--- a/src/dawn/tests/perf_tests/ShaderRobustnessPerf.cpp
+++ b/src/dawn/tests/perf_tests/ShaderRobustnessPerf.cpp
@@ -129,9 +129,9 @@
 
             // Define the region within the current tile that this thread
             // is responsible for loading into the cache.
-            let ColPerThreadA : u32 = TileInner / kWorkgroupSizeX;
+            const ColPerThreadA : u32 = TileInner / kWorkgroupSizeX;
             let tileColA : u32 = local_id.x * ColPerThreadA;
-            let RowPerThreadB : u32 = TileInner / kWorkgroupSizeY;
+            const RowPerThreadB : u32 = TileInner / kWorkgroupSizeY;
             let tileRowB : u32 = local_id.y * RowPerThreadB;
 
             // Loop over shared dimension.
@@ -305,7 +305,7 @@
             var BCached : array<VecT, ColPerThread>;
 
             var globalColA : u32 = tileCol;
-            let RowPerThreadB : u32 = TileInner / kWorkgroupSizeY;
+            const RowPerThreadB : u32 = TileInner / kWorkgroupSizeY;
             let tileRowB : u32 = local_id.y * RowPerThreadB;
 
             // Loop over shared dimension.