Build MojoRunnerApptests.apk for mojo_apptests target on Android.

The FYI 'Chromium Mojo Android' bot is failing the apptests step:
https://build.chromium.org/p/chromium.mojo/builders/Chromium%20Mojo%20Android
..."MojoRunnerApptests.apk is neither a directory nor file"...

Also add other apptest targets from mojo:tests.

BUG=NONE
TEST=FYI bot gets closer to passing apptests step.
R=sky@chromium.org
TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/1683063003

Cr-Commit-Position: refs/heads/master@{#374821}

diff --git a/BUILD.gn b/BUILD.gn
index ba4143e..ce698a7 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -604,10 +604,16 @@
       "//components/resource_provider:resource_provider_unittests",
       "//mash/wm:tests",
       "//media/mojo/services:tests",
+      "//mojo/services/network:apptests",
+      "//mojo/shell:apptests",
       "//sql/mojo:apptests",
       "//ui/views/mus:tests",
     ]
   }
+
+  if (is_android) {
+    deps += [ "//mojo/shell/standalone:mojo_shell_standalone_apptests_apk" ]
+  }
 }
 
 group("gn_only") {