Add missing Proguard rule for library R class.

The framework attempts to call {manifest_package}.R.onResourcesLoaded()
when an APK that is built as a library (typically WebView) is run as a
standalone app, which is intended to fix the R class references to point
to the correct package ID.

We usually already generate the required class/method, but we weren't
keeping it during proguard. Fixing this by adding the missing keep rule
and ensuring that we always generate a class with the right package
means that code running in the context of the WebView APK should now be
able to refer to resources normally via the R class without needing to
use getIdentifier.

Bug: 1009982
Change-Id: Ib33d59ca2696ba949536be34c997690a310c2370
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1834042
Commit-Queue: Richard Coles <torne@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702861}

build/android/gyp/compile_resources.py

@@ -23,6 +23,7 @@ import shutil
 import subprocess
 import sys
 import tempfile
+import textwrap
 import zipfile
 from xml.etree import ElementTree
 
@@ -657,6 +658,8 @@ def _PackageApk(options, build):
   Args:
     options: The command-line options.
     build: BuildContext object.
+  Returns:
+    The manifest package name for the APK.
   """
   dep_subdirs = resource_utils.ExtractDeps(options.dependencies_res_zips,
                                            build.deps_dir)
@@ -763,6 +766,19 @@ def _PackageApk(options, build):
 
   build_utils.CheckOutput(link_command, print_stdout=False, print_stderr=False)
 
+  if options.proguard_file and (options.shared_resources
+                                or options.app_as_shared_lib):
+    # Make sure the R class associated with the manifest package does not have
+    # its onResourcesLoaded method obfuscated or removed, so that the framework
+    # can call it in the case where the APK is being loaded as a library.
+    with open(build.proguard_path, 'a') as proguard_file:
+      keep_rule = '''
+                  -keep class {package}.R {{
+                    public static void onResourcesLoaded(int);
+                  }}
+                  '''.format(package=desired_manifest_package_name)
+      proguard_file.write(textwrap.dedent(keep_rule))
+
   if options.proto_path and options.arsc_path:
     build_utils.CheckOutput([
         options.aapt2_path, 'convert', '-o', build.arsc_path, build.proto_path
@@ -775,6 +791,8 @@ def _PackageApk(options, build):
     _OptimizeApk(build.optimized_arsc_path, options, build.temp_dir,
                  build.arsc_path, build.r_txt_path)
 
+  return desired_manifest_package_name
+
 
 def _OptimizeApk(output, options, temp_dir, unoptimized_path, r_txt_path):
   """Optimize intermediate .ap_ file with aapt2.
@@ -897,7 +915,7 @@ def main(args):
     build_utils.MakeDirectory(debug_temp_resources_dir)
 
   with resource_utils.BuildContext(debug_temp_resources_dir) as build:
-    _PackageApk(options, build)
+    manifest_package_name = _PackageApk(options, build)
 
     # If --shared-resources-whitelist is used, the all resources listed in
     # the corresponding R.txt file will be non-final, and an onResourcesLoaded()
@@ -929,11 +947,16 @@ def main(args):
       custom_root_package_name = options.package_name
       grandparent_custom_package_name = options.r_java_root_package_name
 
+    if options.shared_resources or options.app_as_shared_lib:
+      package_for_library = manifest_package_name
+    else:
+      package_for_library = None
+
     resource_utils.CreateRJavaFiles(
-        build.srcjar_dir, None, build.r_txt_path, options.extra_res_packages,
-        options.extra_r_text_files, rjava_build_options, options.srcjar_out,
-        custom_root_package_name, grandparent_custom_package_name,
-        options.extra_main_r_text_files)
+        build.srcjar_dir, package_for_library, build.r_txt_path,
+        options.extra_res_packages, options.extra_r_text_files,
+        rjava_build_options, options.srcjar_out, custom_root_package_name,
+        grandparent_custom_package_name, options.extra_main_r_text_files)
 
     build_utils.ZipDir(build.srcjar_path, build.srcjar_dir)