Add support for accelerated fixed root background

Tools/DumpRenderTree/chromium/TestShell.cpp

Index: Tools/DumpRenderTree/chromium/TestShell.cpp
diff --git a/Tools/DumpRenderTree/chromium/TestShell.cpp b/Tools/DumpRenderTree/chromium/TestShell.cpp
index 942ec1dcafc0e7f64ef80eb0310920f150a9fb8d..0b32ca691969f98868953d1a74ab384b0df5c294 100644
--- a/Tools/DumpRenderTree/chromium/TestShell.cpp
+++ b/Tools/DumpRenderTree/chromium/TestShell.cpp
@@ -110,6 +110,7 @@ TestShell::TestShell()
     , m_acceleratedCompositingForVideoEnabled(false)
     , m_acceleratedCompositingForFixedPositionEnabled(false)
     , m_acceleratedCompositingForOverflowScrollEnabled(false)
+    , m_acceleratedCompositingForFixedRootBackgroundEnabled(false)
     , m_softwareCompositingEnabled(false)
     , m_threadedCompositingEnabled(false)
     , m_forceCompositingMode(false)
@@ -217,6 +218,7 @@ void TestShell::resetWebSettings(WebView& webView)
     m_prefs.acceleratedCompositingForVideoEnabled = m_acceleratedCompositingForVideoEnabled;
     m_prefs.acceleratedCompositingForFixedPositionEnabled = m_acceleratedCompositingForFixedPositionEnabled;
     m_prefs.acceleratedCompositingForOverflowScrollEnabled = m_acceleratedCompositingForOverflowScrollEnabled;
+    m_prefs.acceleratedCompositingForFixedRootBackgroundEnabled = m_acceleratedCompositingForFixedRootBackgroundEnabled;
     m_prefs.forceCompositingMode = m_forceCompositingMode;
     m_prefs.accelerated2dCanvasEnabled = m_accelerated2dCanvasEnabled;
     m_prefs.perTilePaintingEnabled = m_perTilePaintingEnabled;