Remove unknown preferences errors in layout tests

LayoutTests/css3/filters/blur-filter-page-scroll.html

Index: LayoutTests/css3/filters/blur-filter-page-scroll.html
diff --git a/LayoutTests/css3/filters/blur-filter-page-scroll.html b/LayoutTests/css3/filters/blur-filter-page-scroll.html
index c9e29a17e61e036a22f10337ae264b45bdc40867..68ff0d84127fa5dceae875262f2e1297161ac242 100644
--- a/LayoutTests/css3/filters/blur-filter-page-scroll.html
+++ b/LayoutTests/css3/filters/blur-filter-page-scroll.html
@@ -9,7 +9,7 @@
         <script>
             if (window.testRunner) {
                 // Force software rendering mode.
-                window.testRunner.overridePreference("WebKitAcceleratedCompositingEnabled", "0");
+                window.testRunner.overridePreference("acceleratedCompositingEnabled", "0");

[Julien - ping for review, 2014/08/11 21:28:34]

It turns out that this setting is not recognized by content_shell, that has a
white-list of known settings (that's different from settings.in).

I talked with enne about the best way forward and we should just remove these
overrides as there is no hardware acceleration involved in the tests (we checked
manually).

                 window.testRunner.waitUntilDone();
             }
         </script>