Turn the utility process image decoder into a Mojo service.

components/BUILD.gn

Index: components/BUILD.gn
diff --git a/components/BUILD.gn b/components/BUILD.gn
index 78210393ed1933808aa553264330798cdb3e64a1..e01c7de5cb04585779e9f6d1705a031994da2298 100644
--- a/components/BUILD.gn
+++ b/components/BUILD.gn
@@ -321,7 +321,10 @@ test("components_unittests") {
   }
 
   if (!is_ios) {
-    deps += [ "//components/scheduler:unit_tests" ]
+    deps += [
+      "//components/image_decoder:unit_tests",
+      "//components/scheduler:unit_tests",
+    ]
   }
 }