[fuchsia] Add tests for Fuchsia-specific layer behavior.

Inspect commands going to Scenic and make sure
they match what is expected.

Author: mikejurka

flow/BUILD.gn

@@ -86,6 +86,7 @@ source_set("flow") {
 
     if (using_fuchsia_sdk) {
       public_deps += [
+        "$fuchsia_sdk_root/fidl:fuchsia.ui.app",
         "$fuchsia_sdk_root/fidl:fuchsia.ui.gfx",
         "$fuchsia_sdk_root/pkg:scenic_cpp",
       ]
@@ -156,6 +157,10 @@ executable("flow_unittests") {
     "texture_unittests.cc",
   ]
 
+  if (is_fuchsia) {
+    sources += ["layers/fuchsia_layer_unittests.cc",]
+  }
+
   deps = [
     ":flow",
     ":flow_fixtures",
@@ -167,6 +172,10 @@ executable("flow_unittests") {
     "//third_party/googletest:gtest",
     "//third_party/skia",
   ]
+
+  if (is_fuchsia) {
+    deps += ["//build/fuchsia/pkg:sys_cpp_testing",]
+  }
 }
 
 if (is_fuchsia) {

flow/layers/child_scene_layer.cc

@@ -51,7 +51,7 @@ void ChildSceneLayer::UpdateScene(SceneUpdateContext& context) {
   FML_DCHECK(view_holder);
 
   view_holder->UpdateScene(context, offset_, size_,
-                           sk_float_round2int(context.alphaf() * 255),
+                           SkScalarRoundToInt(context.alphaf() * 255),
                            hit_testable_);
 }