[fuchsia] Modify manifest generation to use partial CMX files.

* Modify all the *sandbox_policy files to be partial CMX files and
  rename them to <package_name>.cmx
* Modify the final CMX generation to merge in the package-supplied
  partial CMX file rather than treat its content as the "sandbox"
  section of the final CMX.
* Rename the |sandbox_policy| parameter for the fuchsia_package GN
  template to |manifest|

Bug: 979830
Change-Id: I7dc466484139db7f62bfe6a713bcfe3ac22b1a2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1682556
Reviewed-by: John Budorick <[email protected]>
Reviewed-by: Sergey Ulanov <[email protected]>
Reviewed-by: Luke Halliwell <[email protected]>
Reviewed-by: Sami Kyöstilä <[email protected]>
Commit-Queue: Fabrice de Gans-Riberi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#675396}
diff --git a/testing/test.gni b/testing/test.gni
index 84796d21..5ad48c9e1 100644
--- a/testing/test.gni
+++ b/testing/test.gni
@@ -278,7 +278,7 @@
 
     fuchsia_package(_pkg_target) {
       testonly = true
-      forward_variables_from(invoker, [ "sandbox_policy" ])
+      forward_variables_from(invoker, [ "manifest" ])
       binary = ":$_exec_target"
       package_name_override = _output_name
     }