[fuchsia] Implement the fuchsia.web.Debug API

* Add support for test suite-specific sandbox policy.
* Add fuchsia.web.Debug API to the ContextProvider service.
* Add tests for that API by using the Fuchsia Hub.

Bug: 955589
Change-Id: Icc5d9a91c30b55e71f6f104f8b7ea984b811a1a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578597
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665620}

diff --git a/testing/test.gni b/testing/test.gni
index 563586d..9fb6865 100644
--- a/testing/test.gni
+++ b/testing/test.gni

@@ -274,17 +274,18 @@
       ]
     }
 
+    fuchsia_package(_pkg_target) {
+      testonly = true
+      forward_variables_from(invoker, [ "sandbox_policy" ])
+      binary = ":$_exec_target"
+      package_name_override = _output_name
+    }
+
     executable(_exec_target) {
       forward_variables_from(invoker, "*")
       testonly = true
       output_name = _exec_target
     }
-
-    fuchsia_package(_pkg_target) {
-      testonly = true
-      binary = ":$_exec_target"
-      package_name_override = _output_name
-    }
   } else if (is_ios) {
     import("//build/config/ios/ios_sdk.gni")
     import("//build/config/ios/rules.gni")