Add resource whitelisting to android_webview pak files.

android_webview/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 import("//build/config/locales.gni")
 import("//tools/grit/repack.gni")
+import("//tools/resources/generate_resource_whitelist.gni")
 import("system_webview_apk_tmpl.gni")
 import("webview_repack_locales.gni")
 
 declare_args() {
   # Package name of the system_webview_apk target.
   system_webview_package_name = "com.android.webview"
 }
 
 if (!defined(use_webview_internal_framework)) {
   use_webview_internal_framework = false
 }
 
+if (enable_resource_whitelist_generation) {
+  system_webview_pak_whitelist =
+      "$target_gen_dir/system_webview_pak_whitelist.txt"
+}
+
 system_webview_android_manifest =
     "$target_gen_dir/system_webview_apk/AndroidManifest.xml"
 
 group("android_webview") {
   if (!use_webview_internal_framework) {
     deps = [
       ":system_webview_apk",
     ]
   }
 }
 
 jinja_template("system_webview_manifest") {
   input = "apk/java/AndroidManifest.xml"
   output = system_webview_android_manifest
   variables = [ "package=$system_webview_package_name" ]
 }
 
 webview_repack_locales("repack_locales") {
   input_locales = locales
   output_locales = locales
+
+  if (enable_resource_whitelist_generation) {
+    repack_whitelist = system_webview_pak_whitelist
+    deps = [
+      ":system_webview_pak_whitelist",
+    ]
+  }
 }
 
 locale_pak_resources("locale_paks") {
   sources = [
     "$root_out_dir/android_webview/locales/am.pak",
     "$root_out_dir/android_webview/locales/ar.pak",
     "$root_out_dir/android_webview/locales/bg.pak",
     "$root_out_dir/android_webview/locales/bn.pak",
     "$root_out_dir/android_webview/locales/ca.pak",
     "$root_out_dir/android_webview/locales/cs.pak",
@@ skipping 57 matching lines @@
     "$root_gen_dir/net/net_resources.pak",
     "$target_gen_dir/aw_resources.pak",
   ]
   deps = [
     ":generate_aw_resources",
     "//content:resources",
     "//net:net_resources",
     "//third_party/WebKit/public:resources",
   ]
   output = "$target_gen_dir/resources.pak"
+
+  if (enable_resource_whitelist_generation) {
+    repack_whitelist = system_webview_pak_whitelist
+    deps += [ ":system_webview_pak_whitelist" ]
+  }
 }
 
 repack("repack_100_percent") {
   sources = [
     "$root_gen_dir/blink/public/resources/blink_image_resources_100_percent.pak",
     "$root_gen_dir/content/app/resources/content_resources_100_percent.pak",
     "$root_gen_dir/ui/resources/ui_resources_100_percent.pak",
   ]
   deps = [
     "//content/app/resources",
     "//third_party/WebKit/public:image_resources",
     "//ui/resources",
   ]
   output = "$target_gen_dir/chrome_100_percent.pak"
+
+  if (enable_resource_whitelist_generation) {
+    repack_whitelist = system_webview_pak_whitelist
+    deps += [ ":system_webview_pak_whitelist" ]
+  }
 }
 
 webview_license_path = "$target_gen_dir/webview_licenses.notice"
 
 android_assets("pak_file_assets") {
   sources = [
     "$target_gen_dir/chrome_100_percent.pak",
     "$target_gen_dir/resources.pak",
   ]
   deps = [
@@ skipping 119 matching lines @@
     "aw_strings_zh-TW.pak",
   ]
 }
 
 grit("generate_components_strings") {
   source = "../components/components_strings.grd"
 
   # components_strings contains strings from all components. WebView
   # will never display most of them, so we try to limit the included
   # strings
   whitelist = rebase_path("ui/grit_components_whitelist.txt")

[michaelbai, 2016/09/19 21:02:06]

Here, we manually add whitelist, would you mind to find out why ui directory has
this list? Should it be removed? what's relationship between this and your
change?

[agrieve, 2016/09/20 00:48:34]

Wow, didn't even notice this. Tested removing it, and it looks like it still
does a lot. This means that it strips out resources that are unreached, but
still seen by the compiler because they are not #ifdef'ed out. Added a comment.

[michaelbai, 2016/09/20 01:01:01]

It probably means we could do more to remove the unused resources? Will file a
bug on this.

[agrieve, 2016/09/20 01:08:58]

It's certainly possible. Right now if the compiler sees an ID at all, it marks
it as used. Even if it's in dead code.

   inputs = [
     whitelist,
   ]
   grit_flags = [
     "-w",
     whitelist,
   ]
   outputs = [
     "grit/components_strings.h",
     "components_strings_am.pak",
@@ skipping 115 matching lines @@
 
 if (android_64bit_target_cpu) {
   shared_library("monochrome") {
     deps = [
       ":webview_entry_point",
     ]
     configs -= [ "//build/config/android:hide_native_jni_exports" ]
   }
 }
 
+if (enable_resource_whitelist_generation) {
+  generate_resource_whitelist("system_webview_pak_whitelist") {
+    deps = [
+      ":libwebviewchromium",
+    ]
+    input = "$root_out_dir/libwebviewchromium$shlib_extension.whitelist"

[michaelbai, 2016/09/19 19:06:13]

Sorry, I missed context here, could you show me where shlib_extension.whitelist
is defined and how lib_foo.$shlib_extension.whitelist is generated? I searched
code and can't figure it out.

[agrieve, 2016/09/19 19:10:32]

Searching for "enable_resource_whitelist_generation" is the key here.
This causes whitelists to be created as a part of compilation:
https://cs.chromium.org/chromium/src/build/toolchain/gcc_toolchain.gni?q=enab...

It doesn't solve the problem of excessive pragma warnings, but does at least
scope usages to specific .o files. Then, when linking the .o.whitelist files are
concatenated together.

This final generate_resource_whitelist() step actually just adds in 2 hard-coded
resource IDs on top of the .so.whitelist one.

[michaelbai, 2016/09/19 21:02:06]

Thanks for your explanation, now I understand how it works, but still have one
question, is shlib_extension.whitelist defined anywhere?

[agrieve, 2016/09/20 00:48:34]

shlib_extension is defined here: build/toolchain/toolchain.gni
.whitelist isn't a part of the expression (it's the file extension)

+    output = system_webview_pak_whitelist
+  }
+}
+
 source_set("common") {
   sources = [
     "browser/aw_browser_context.cc",
     "browser/aw_browser_context.h",
     "browser/aw_browser_main_parts.cc",
     "browser/aw_browser_main_parts.h",
     "browser/aw_browser_permission_request_delegate.h",
     "browser/aw_browser_policy_connector.cc",
     "browser/aw_browser_policy_connector.h",
     "browser/aw_content_browser_client.cc",
@@ skipping 371 matching lines @@
   system_webview_apk_tmpl("system_webview_apk") {
     android_manifest = system_webview_android_manifest
     android_manifest_dep = ":system_webview_manifest"
     deps = [
       ":system_webview_resources",
       "//android_webview/glue",
     ]
     apk_name = "SystemWebView"
   }
 }