Most css1/ tests should wait for basebg.gif to be loaded

third_party/WebKit/LayoutTests/VirtualTestSuites

 [
   {
     "prefix": "color_space",
     "base": "fast/canvas/color-space",
     "args": ["--enable-color-correct-rendering",
              "--enable-true-color-rendering"]
   },
   {
     "prefix": "gpu",
     "base": "fast/canvas",
@@ skipping 273 matching lines @@
     "prefix": "mojo-loading",
     "base": "webexposed",
     "args": ["--enable-blink-features=LoadingWithMojo"]
   },
   {
     "prefix": "mojo-loading",
     "base": "http/tests",
     "args": ["--enable-blink-features=LoadingWithMojo"]
   },
   {
+    "prefix": "mojo-loading",
+    "base": "css1",
+    "args": ["--enable-blink-features=LoadingWithMojo"]
+  },
+  {
     "prefix": "scalefactor150",
     "base": "fast/events/synthetic-events",
     "args": ["--force-device-scale-factor=1.5"]
   },
   {
     "prefix": "enable_wasm",
     "base": "http/tests/wasm",
     "args": ["--enable-features=WebAssembly"]
   },
   {
@@ skipping 50 matching lines @@
     "prefix": "spinvalidation",
     "base": "paint",
     "args": ["--enable-blink-features=SlimmingPaintInvalidation"]
   },
   {
     "prefix": "spinvalidation",
     "base": "svg",
     "args": ["--enable-blink-features=SlimmingPaintInvalidation"]
   }
 ]