Move all wallpaper file loading and decoding from DesktopBackgroundController to WallpaperManager.

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index 21bbbd70c5bcf4ee1e248c73001519a8ac773992..49f1d08077e750f8cfc793373c7302c3a9d3e66b 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -207,22 +207,12 @@ aura::test::EventGenerator& AshTestBase::GetEventGenerator() {
   return *event_generator_.get();
 }
 
-// static
 bool AshTestBase::SupportsMultipleDisplays() {
-#if defined(OS_WIN)
-  return base::win::GetVersion() < base::win::VERSION_WIN8;
-#else
-  return true;
-#endif
+  return AshTestHelper::SupportsMultipleDisplays();
 }
 
-// static
 bool AshTestBase::SupportsHostWindowResize() {
-#if defined(OS_WIN)
-  return base::win::GetVersion() < base::win::VERSION_WIN8;
-#else
-  return true;
-#endif
+  return AshTestHelper::SupportsHostWindowResize();
 }
 
 void AshTestBase::UpdateDisplay(const std::string& display_specs) {