More SynchronousInterfacePtr conversion + some related pexe content handler cleanup.

services/http_server/BUILD.gn

Index: services/http_server/BUILD.gn
diff --git a/services/http_server/BUILD.gn b/services/http_server/BUILD.gn
index 3ac29a952055c118dd2662c3fcf9c3360163c5ae..4b2c7244d0151245c285127648420c470629b115 100644
--- a/services/http_server/BUILD.gn
+++ b/services/http_server/BUILD.gn
@@ -60,8 +60,11 @@ mojo_native_application("apptests") {
     "//mojo/public/cpp/system",
     "//mojo/services/http_server/cpp",
     "//mojo/services/http_server/interfaces",
+    "//mojo/services/http_server/interfaces:interfaces_sync",
     "//mojo/services/network/interfaces",
   ]
 
-  data_deps = [ ":http_server($default_toolchain)" ]
+  data_deps = [
+    ":http_server($default_toolchain)",
+  ]
 }