[tint][utils] Add missing const to Slice equality operator

Change-Id: Iff5cc9761e26e7668cdfbc75f581203b54c88227
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/174282
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Auto-Submit: Ben Clayton <bclayton@google.com>

src/tint/utils/containers/slice.h

diff --git a/src/tint/utils/containers/slice.h b/src/tint/utils/containers/slice.h
index 3c60913..89afcb1 100644
--- a/src/tint/utils/containers/slice.h
+++ b/src/tint/utils/containers/slice.h
@@ -276,14 +276,14 @@
     /// Equality operator.
     /// @param other the other slice to compare against
     /// @returns true if all fields of this slice are equal to the fields of @p other
-    bool operator==(const Slice& other) {
+    bool operator==(const Slice& other) const {
         return data == other.data && len == other.len && cap == other.cap;
     }
 
     /// Inequality operator.
     /// @param other the other slice to compare against
     /// @returns false if any fields of this slice are not equal to the fields of @p other
-    bool operator!=(const Slice& other) { return !(*this == other); }
+    bool operator!=(const Slice& other) const { return !(*this == other); }
 };
 
 /// Deduction guide for Slice from c-array

src/tint/utils/containers/slice_test.cc

diff --git a/src/tint/utils/containers/slice_test.cc b/src/tint/utils/containers/slice_test.cc
index 01932fd..5e30d4e 100644
--- a/src/tint/utils/containers/slice_test.cc
+++ b/src/tint/utils/containers/slice_test.cc
@@ -206,7 +206,7 @@
 
 TEST(TintSliceTest, Equality) {
     int elements[] = {1, 2, 3};
-    auto a = Slice{elements};
+    const auto a = Slice{elements};
     {
         auto b = a;
         EXPECT_TRUE(a == b);