IndexedDB: Fix WPT bindings-inject-key to clean up Object.prototype

chromedriver doesn't allow changing Object.prototype to add enumerable
properties, but this test requires setting some values on
Object.prototype.  When Object.prototype.a is set to:

  {b: {c: 'on proto'}}

chromedriver fails with:

    JavascriptErrorException: javascript error (500): Maximum call stack size exceeded
      (Session info: chrome=72.0.3626.121)

    Remote-end stacktrace:

    #0 0x563ff3a32a59 <unknown>
    #1 0x563ff39cb7f3 <unknown>
    #2 0x563ff38fcd7c <unknown>
    #3 0x563ff38ff78c <unknown>
    #4 0x563ff38ff5f7 <unknown>
    #5 0x563ff38ffbe7 <unknown>
    #6 0x563ff38fff1b <unknown>
    #7 0x563ff38a3f7a <unknown>
    #8 0x563ff3899bf2 <unknown>
    #9 0x563ff38a37b7 <unknown>
    #10 0x563ff3899ac3 <unknown>
    #11 0x563ff38782d2 <unknown>
    #12 0x563ff3879112 <unknown>
    #13 0x563ff39fe865 <unknown>
    web-platform-tests#14 0x563ff39ff32b <unknown>
    web-platform-tests#15 0x563ff39ff70c <unknown>
    web-platform-tests#16 0x563ff39d940a <unknown>
    web-platform-tests#17 0x563ff39ff997 <unknown>
    web-platform-tests#18 0x563ff39e9947 <unknown>
    web-platform-tests#19 0x563ff3a1a800 <unknown>
    web-platform-tests#20 0x563ff3a3c8be <unknown>
    web-platform-tests#21 0x7f3bf4545494 start_thread
    web-platform-tests#22 0x7f3bf2d58a8f clone

    Ran 1 tests finished in 2.0 seconds.
      • 0 ran as expected. 0 tests skipped.
      • 1 tests had errors unexpectedly

Work around this problem by cleaning up the test environment so
Object.prototype no longer has the override by the time chromedriver
tries to inspect the test result.

While here, fix the other tests to use the t.add_cleanup() function
so they'll cleanup their test environment in case they exit in
some other way besides reaching t.done().

The underlying chromedriver issue is tracked upstream at
https://crbug.com/chromedriver/2555.

Bug: 934844
Change-Id: Id1b4ab2a908bfbc001e2a2d045eeec3ef01c24d9

IndexedDB/bindings-inject-key.html

@@ -21,6 +21,9 @@
       configurable: true,
       set: t.step_func((value) => { setter_called = true; }),
     });
+    t.add_cleanup(function() {
+      delete Object.prototype['10'];
+    });
     request.onerror = t.unreached_func('request should not fail');
     request.onsuccess = t.step_func(() => {
       const result = request.result;
@@ -31,8 +34,6 @@
           'Result should have own-property overriding prototype setter.');
       assert_equals(result[10], 'key',
                     'Result should have expected property.');
-
-      delete Object.prototype['10'];
       t.done();
     });
   },
@@ -53,6 +54,9 @@
       configurable: true,
       set: t.step_func(function(value) { setter_called = true; }),
     });
+    t.add_cleanup(function() {
+      delete Object.prototype['id'];
+    });
     request.onerror = t.unreached_func('request should not fail');
     request.onsuccess = t.step_func(function() {
         const result = request.result;
@@ -63,8 +67,6 @@
           'Result should have own-property overriding prototype setter.');
       assert_equals(result.id, 1,
                     'Own property should match primary key generator value');
-
-      delete Object.prototype['id'];
       t.done();
     });
   },
@@ -81,6 +83,11 @@
     const request = tx.objectStore('store').get(1);
 
     Object.prototype.a = {b: {c: 'on proto'}};
+    t.add_cleanup(function() {
+      delete Object.prototype.a;
+    });
+    assert_equals(Object.prototype.a.b.c, 'on proto',
+                  'Prototype should be configured for test');
 
     request.onerror = t.unreached_func('request should not fail');
     request.onsuccess = t.step_func(function() {
@@ -94,7 +101,7 @@
       assert_equals(result.a.b.c, 1,
                     'Own property should match primary key generator value');
       assert_equals(Object.prototype.a.b.c, 'on proto',
-                  'Prototype should not be modified');
+                    'Prototype should not be modified');
       t.done();
     });
   },