[worklets] Introduce ThreadedWorkletMessagingProxy and AnimationWorkletMessagaingProxy.

third_party/WebKit/LayoutTests/VirtualTestSuites

 [
   {
     "prefix": "gpu",
     "base": "fast/canvas",
     "args": ["--enable-accelerated-2d-canvas",
              "--disable-display-list-2d-canvas"]
   },
   {
     "prefix": "display_list_2d_canvas",
     "base": "fast/canvas",
     "args": ["--force-display-list-2d-canvas"]
   },
   {
     "prefix": "threaded",
     "base": "compositing/visibility",
     "args": ["--enable-threaded-compositing"]
   },
   {
     "prefix": "threaded",
     "base": "fast/compositorworker",
     "args": ["--enable-threaded-compositing"]
   },
   {
     "prefix": "threaded",
+    "base": "http/tests/worklet",
+    "args": ["--enable-threaded-compositing"]
+  },
+  {
+    "prefix": "threaded",
     "base": "compositing/webgl",
     "args": ["--enable-threaded-compositing"]
   },
   {
     "prefix": "prefer_compositing_to_lcd_text",
     "base": "compositing/overflow",
     "args": ["--enable-prefer-compositing-to-lcd-text"]
   },
   {
     "prefix": "prefer_compositing_to_lcd_text",
@@ skipping 253 matching lines @@
     "prefix": "enable_wasm",
     "base": "http/tests/wasm",
     "args": ["--enable-wasm"]
   },
   {
     "prefix": "mojo-service-worker",
     "base": "http/tests/serviceworker",
     "args": ["--mojo-service-worker"]
   }
 ]