wpt: Add tests for independent localStorage/sessionStorage quotas

The new tests verify that exhausting the quota of one Web Storage area does
not significantly reduce the capacity available to the other one.

Each test first measures the baseline capacity of one storage type by filling
it until QuotaExceededError is thrown, then clears it, exhausts the other
storage type, and measures the capacity again. Independence is verified by
requiring that the second measurement remains broadly comparable to the
baseline rather than collapsing to near-zero capacity, which would indicate
a shared quota.

Two directional tests are added:
- sessionStorage retains comparable quota after localStorage exhaustion
- localStorage retains comparable quota after sessionStorage exhaustion

Gecko currently fails these new tests. This is consistent with the fact that
the existing quota exhaustion tests also currently fail in Gecko.

Signed-off-by: Jan Varga <[email protected]>

Author: janvarga

webstorage/storage_local_quota_independent_from_session.window.js

@@ -0,0 +1,43 @@
+test(t => {
+    localStorage.clear();
+    sessionStorage.clear();
+
+    var key = "name";
+    var val = "x".repeat(4 * 1024);
+
+    t.add_cleanup(() => {
+        localStorage.clear();
+        sessionStorage.clear();
+    });
+
+    let indexBefore = 0;
+    assert_throws_quotaexceedederror(() => {
+        while (true) {
+            localStorage.setItem("" + key + indexBefore, "" + val + indexBefore);
+            indexBefore++;
+        }
+    }, null, null);
+
+    localStorage.clear();
+
+    let indexLocal = 0;
+    assert_throws_quotaexceedederror(() => {
+        while (true) {
+            sessionStorage.setItem("" + key + indexLocal, "" + val + indexLocal);
+            indexLocal++;
+        }
+    }, null, null);
+
+    let indexAfter = 0;
+    assert_throws_quotaexceedederror(() => {
+        while (true) {
+            localStorage.setItem("" + key + indexAfter, "" + val + indexAfter);
+            indexAfter++;
+        }
+    }, null, null);
+
+    assert_greater_than_equal(
+        indexAfter,
+        Math.floor(indexBefore / 2)
+    );
+}, "localStorage retains comparable quota after sessionStorage exhaustion");

webstorage/storage_session_quota_independent_from_local.window.js

@@ -0,0 +1,43 @@
+test(t => {
+    sessionStorage.clear();
+    localStorage.clear();
+
+    var key = "name";
+    var val = "x".repeat(4 * 1024);
+
+    t.add_cleanup(() => {
+        sessionStorage.clear();
+        localStorage.clear();
+    });
+
+    let indexBefore = 0;
+    assert_throws_quotaexceedederror(() => {
+        while (true) {
+            sessionStorage.setItem("" + key + indexBefore, "" + val + indexBefore);
+            indexBefore++;
+        }
+    }, null, null);
+
+    sessionStorage.clear();
+
+    let indexLocal = 0;
+    assert_throws_quotaexceedederror(() => {
+        while (true) {
+            localStorage.setItem("" + key + indexLocal, "" + val + indexLocal);
+            indexLocal++;
+        }
+    }, null, null);
+
+    let indexAfter = 0;
+    assert_throws_quotaexceedederror(() => {
+        while (true) {
+            sessionStorage.setItem("" + key + indexAfter, "" + val + indexAfter);
+            indexAfter++;
+        }
+    }, null, null);
+
+    assert_greater_than_equal(
+        indexAfter,
+        Math.floor(indexBefore / 2)
+    );
+}, "sessionStorage retains comparable quota after localStorage exhaustion");