Use R.txt from AAR to generate R.java for it when building APK.

build/android/gyp/process_resources.py

Index: build/android/gyp/process_resources.py
diff --git a/build/android/gyp/process_resources.py b/build/android/gyp/process_resources.py
index 2d4638f8d81f77dca0dacb705e4ca9fbdc5959cf..0f68866647b26d6bf1877f0c3486bcb829f034f6 100755
--- a/build/android/gyp/process_resources.py
+++ b/build/android/gyp/process_resources.py
@@ -74,7 +74,11 @@ def _ParseArgs(args):
   parser.add_option('--srcjar-out',
                     help='Path to srcjar to contain generated R.java.')
   parser.add_option('--r-text-out',
-                    help='Path to store the R.txt file generated by appt.')
+                    help='Path to store the generated R.txt file.')
+  parser.add_option('--r-text-in',
+                    help='Path to pre-existing R.txt for these resources. '
+                    'Resource names from it will be used to generate R.java '
+                    'instead of aapt-generated R.txt.')
 
   parser.add_option('--proguard-file',
                     help='Path to proguard.txt generated file')
@@ -169,8 +173,24 @@ def CreateRJavaFiles(srcjar_dir, main_r_txt_file, packages, r_txt_files,
     # figure out which entries belong to them, but use the values from the
     # main R.txt file.
     for entry in _ParseTextSymbolsFile(r_txt_file):
-      entry = all_resources[(entry.resource_type, entry.name)]
-      resources_by_type[entry.resource_type].append(entry)
+      entry = all_resources.get((entry.resource_type, entry.name))
+      # For most cases missing entry here is an error. It means that some
+      # library claims to have or depend on a resource that isn't included into
+      # the APK. There is one notable exception: Google Play Services (GMS).
+      # GMS is shipped as a bunch of AARs. One of them - basement - contains
+      # R.txt with ids of all resources, but most of the resources are in the
+      # other AARs. However, all other AARs reference their resources via
+      # basement's R.java so the latter must contain all ids that are in its
+      # R.txt. Most targets depend on only a subset of GMS AARs so some
+      # resources are missing, which is okay because the code that references
+      # them is missing too. We can't get an id for a resource that isn't here
+      # so the only solution is to skip the resource entry entirely.
+      #
+      # We can verify that all entries referenced in the code were generated
+      # correctly by running Proguard on the APK: it will report missing
+      # fields.
+      if entry:
+        resources_by_type[entry.resource_type].append(entry)
 
   for package, resources_by_type in resources_by_package.iteritems():
     package_r_java_dir = os.path.join(srcjar_dir, *package.split('.'))
@@ -432,6 +452,12 @@ def _OnStaleMd5(options):
       build_utils.Touch(r_txt_path)
 
     if not options.include_all_resources:
+      # --include-all-resources can only be specified for generating final R
+      # classes for APK. It makes no sense for APK to have pre-generated R.txt
+      # though, because aapt-generated already lists all available resources.
+      if options.r_text_in:
+        r_txt_path = options.r_text_in
+
       packages = list(options.extra_res_packages)
       r_txt_files = list(options.extra_r_text_files)