Refactor WebView APK dependencies.

Move the "common" dependencies that are used by all
system_webview_apk_tmpl users into the actual template to avoid
repeating them in multiple places (upstream and downstream), and move
the ones that are only used upstream into a variable to make it clearer
that developers shouldn't add new dependencies to the target itself.

This avoids mistakes where the dependency list upstream and downstream
can get out of sync, and will allow Trichrome to reuse the dependencies
as well.

Change-Id: I415180dd42915ba7ea3cc271f330d97b4e250b23
Reviewed-on: https://chromium-review.googlesource.com/1240976Reviewed-by: Changwan Ryu <changwan@chromium.org>
Commit-Queue: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594118}

android_webview/BUILD.gn

@@ -1082,12 +1082,7 @@ if (public_android_sdk) {
     version_name = chrome_version_name
     android_manifest = system_webview_android_manifest
     android_manifest_dep = ":system_webview_manifest"
-    deps = [
-      ":platform_service_bridge_upstream_implementation_java",
-      ":system_webview_resources",
-      "//android_webview/glue",
-      "//android_webview/support_library:support_lib_glue_java",
-    ]
+    deps = upstream_only_webview_deps
     apk_name = "SystemWebView"
   }
 }

android_webview/system_webview_apk_tmpl.gni

@@ -15,6 +15,8 @@ template("system_webview_apk_tmpl") {
       "//android_webview:assets",
       "//android_webview/apk:webview_license_activity_java",
       "//android_webview/apk:webview_license_provider_java",
+      "//android_webview/glue",
+      "//android_webview/support_library:support_lib_glue_java",
       "//base:base_java",
     ]
 

android_webview/variables.gni

@@ -4,3 +4,8 @@
 
 system_webview_android_manifest =
     "$root_gen_dir/android_webview/system_webview_apk/AndroidManifest.xml"
+
+upstream_only_webview_deps = [
+  "//android_webview:platform_service_bridge_upstream_implementation_java",
+  "//android_webview:system_webview_resources",
+]