Overhaul Mandoline event transport code

components/html_viewer/BUILD.gn

Index: components/html_viewer/BUILD.gn
diff --git a/components/html_viewer/BUILD.gn b/components/html_viewer/BUILD.gn
index 2ec830646af22f760b6d3b05f2f01f0ae2513e30..19358b42f9e0b00dd7895f858c5afb030be80736 100644
--- a/components/html_viewer/BUILD.gn
+++ b/components/html_viewer/BUILD.gn
@@ -307,6 +307,7 @@ test("html_viewer_unittests") {
   sources = [
     "ax_provider_impl_unittest.cc",
     "discardable_memory_allocator_unittest.cc",
+    "input_events_unittest.cc",
     "run_all_unittests.cc",
   ]
   deps = [
@@ -315,9 +316,12 @@ test("html_viewer_unittests") {
     "//base/test:test_support",
     "//components/scheduler",
     "//gin",
+    "//mojo/converters/input_events",
     "//testing/gtest:gtest",
     "//third_party/mojo/src/mojo/edk/system",
     "//ui/base",
+    "//ui/events",
+    "//ui/events:test_support",
     "//ui/mojo/init",
   ]