[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/fuchsia/engine/BUILD.gn b/fuchsia/engine/BUILD.gn
index 165a179f..816722a 100644
--- a/fuchsia/engine/BUILD.gn
+++ b/fuchsia/engine/BUILD.gn
@@ -165,7 +165,7 @@
 fuchsia_package("web_engine") {
   binary = ":web_engine_exe"
   package_name_override = "chromium"
-  sandbox_policy = "sandbox_policy"
+  manifest = "web_engine.cmx"
   excluded_files = [
     "lib/libswiftshader_libEGL.so",
     "lib/libswiftshader_libGLESv2.so",
@@ -241,7 +241,7 @@
 }
 
 test("web_engine_integration_tests") {
-  sandbox_policy = "integration_tests_sandbox_policy"
+  manifest = "web_engine_integration_tests.cmx"
   sources = [
     "test_debug_listener.cc",
     "test_debug_listener.h",