Make gradient-eval-* tests fail without lab/lch support

Test references use new color functions. Make sure older implementations
fail by adding a red background fallback in the references.

Bug: 1362022
Change-Id: I873f219f6684c5d391fb9afe90da28408496d65d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3902032
Reviewed-by: Philip Jägenstedt <[email protected]>
Commit-Queue: Philip Jägenstedt <[email protected]>
Auto-Submit: Rune Lillesveen <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1047925}

css/css-images/gradient/gradient-eval-002-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lab(60% 0 0);
    }
  </style>

css/css-images/gradient/gradient-eval-003-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lab(60% 0 0);
    }
  </style>

css/css-images/gradient/gradient-eval-005-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lch(60% 60 0);
    }
  </style>

css/css-images/gradient/gradient-eval-006-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lab(75% 0 0);
    }
  </style>

css/css-images/gradient/gradient-eval-007-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lch(60% 60 0);
    }
  </style>

css/css-images/gradient/gradient-eval-008-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lch(60% 60 0);
    }
  </style>

css/css-images/gradient/gradient-eval-009-ref.html

@@ -7,6 +7,7 @@
    .test {
        width: 100px;
        height: 100px;
+       background: red;
        background: lch(60% 60 0);
    }
  </style>