Expose some sky_viewer plumbing to allow for reuse

sky/viewer/BUILD.gn

Index: sky/viewer/BUILD.gn
diff --git a/sky/viewer/BUILD.gn b/sky/viewer/BUILD.gn
index 20505a9f75603b71cecd94276789ac411a4d163f..fff88a0da308d6d3b019fa6ab2aa7d31b8272c78 100644
--- a/sky/viewer/BUILD.gn
+++ b/sky/viewer/BUILD.gn
@@ -5,12 +5,8 @@
 import("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
-mojo_native_application("viewer") {
-  output_name = "sky_viewer"
-
+source_set("lib") {
   sources = [
-    "content_handler_impl.cc",
-    "content_handler_impl.h",
     "converters/basic_types.cc",
     "converters/basic_types.h",
     "converters/input_event_types.cc",
@@ -21,7 +17,10 @@ mojo_native_application("viewer") {
     "internals.h",
     "runtime_flags.cc",
     "runtime_flags.h",
-    "viewer.cc",
+    "sky_loader.cc",
+    "sky_loader.h",
+    "sky_viewer_base.cc",
+    "sky_viewer_base.h",
   ]
 
   include_dirs = [ ".." ]
@@ -34,9 +33,7 @@ mojo_native_application("viewer") {
     "//mojo/converters/input_events",
     "//mojo/converters/surfaces",
     "//mojo/icu",
-    "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/system",
-    "//mojo/public/cpp/utility",
     "//mojo/public/interfaces/application",
     "//mojo/services/content_handler/public/interfaces",
     "//mojo/services/gpu/public/interfaces",
@@ -45,7 +42,6 @@ mojo_native_application("viewer") {
     "//mojo/services/network/public/interfaces",
     "//mojo/services/service_registry/public/interfaces",
     "//mojo/services/surfaces/public/interfaces",
-    "//mojo/services/view_manager/public/cpp",
     "//mojo/services/view_manager/public/interfaces",
     "//skia",
     "//sky/compositor",
@@ -57,4 +53,31 @@ mojo_native_application("viewer") {
     "//ui/events",
     "//url",
   ]
+
+  public_deps = [
+    "//mojo/services/view_manager/public/cpp",
+  ]
+}
+
+mojo_native_application("viewer") {
+  output_name = "sky_viewer"
+
+  sources = [
+    "content_handler_impl.cc",
+    "content_handler_impl.h",
+    "viewer.cc",
+  ]
+
+  include_dirs = [ ".." ]
+
+  deps = [
+    ":lib",
+    "//base",
+    "//mojo/application",
+    "//mojo/public/cpp/bindings",
+    "//mojo/public/cpp/utility",
+    "//mojo/public/interfaces/application",
+    "//mojo/services/content_handler/public/interfaces",
+    "//mojo/services/network/public/interfaces",
+  ]
 }