Define a unified protobuf message for "aapt2 optimize" metadata.

This helps solve three problems:

* obfuscation maps are now documented.
* obfuscation maps will not require hand-rolled parsers.
* no additional plumbing will be required for future
  optimizations---plumbing individual mapping files in Bazel for
  ProGuard, aapt2, etc. has been a pain.

Bug: 153201806
Test: make aapt2
Change-Id: Ie3829834527e8875d768ae28242d3aeca28c6db2

tools/aapt2/Android.bp

@@ -161,6 +161,7 @@ cc_library_host_static {
         "ApkInfo.proto",
         "Configuration.proto",
         "Resources.proto",
+        "ResourceMetadata.proto",
         "ResourcesInternal.proto",
         "ValueTransformer.cpp",
     ],
@@ -218,6 +219,7 @@ genrule {
     srcs: [
         "Configuration.proto",
         "ResourcesInternal.proto",
+        "ResourceMetadata.proto",
         "Resources.proto",
     ],
     out: ["aapt2-protos.zip"],

tools/aapt2/ResourceMetadata.proto

@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+syntax = "proto3";
+
+package aapt.pb;
+
+option java_package = "com.android.aapt";
+option java_multiple_files = true;
+
+message ResourceMappings {
+  ShortenedPathsMap shortened_paths = 1;
+  CollapsedNamesMap collapsed_names = 2;
+}
+
+// Metadata relating to "aapt2 optimize --shorten-resource-paths"
+message ShortenedPathsMap {
+  // Maps shorted paths (e.g. "res/foo.xml") to their original names (e.g.
+  // "res/xml/file_with_long_name.xml").
+  message ResourcePathMapping {
+    string shortened_path = 1;
+    string original_path = 2;
+  }
+  repeated ResourcePathMapping resource_paths = 1;
+}
+
+// Metadata relating to "aapt2 optimize --collapse-resource-names"
+message CollapsedNamesMap {
+  // Maps resource IDs (e.g. 0x7f123456) to their original names (e.g.
+  // "package:type/entry").
+  message ResourceNameMapping {
+    uint32 id = 1;
+    string name = 2;
+  }
+  repeated ResourceNameMapping resource_names = 1;
+}