Add chain-agents agent

This agent is able to chain-load other agents listed in a given file.
This is useful for testing and using persistent JVMTI agents, which
might need to have specific arguments passed to them.

Test: Install debuggable apk (here com.antonioleiva.bandhookkotlin)
  walleye:/ $ run-as com.antonioleiva.bandhookkotlin sh
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ mkdir code_cache/startup_agents
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ cp /data/local/tmp/libtifasts32.so code_cache
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ cp /data/local/tmp/libtifasts64.so code_cache
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ cp /data/local/tmp/libchainagentss32.so code_cache/startup_agents/
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ cp /data/local/tmp/libchainagentss64.so code_cache/startup_agents/
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ echo $PWD/code_cache/libtifasts32.so=log,ClassLoad > chain_agents.txt
  walleye:/data/data/com.antonioleiva.bandhookkotlin $ echo $PWD/code_cache/libtifasts64.so=log,ClassLoad >> chain_agents.txt
  Start bandhookkotlin
  Examine logcat

Bug: 135627501
Change-Id: Icd97e8cce6c540b8d1ee5e5efd7b2587707786d3
diff --git a/tools/jvmti-agents/chain-agents/Android.bp b/tools/jvmti-agents/chain-agents/Android.bp
new file mode 100644
index 0000000..148082d
--- /dev/null
+++ b/tools/jvmti-agents/chain-agents/Android.bp
@@ -0,0 +1,84 @@
+//
+// Copyright (C) 2019 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.
+//
+
+// Build variants {target,host} x {debug,ndebug} x {32,64}
+
+cc_defaults {
+    name: "chainagents-base-defaults",
+    srcs: ["chainagents.cc"],
+    defaults: ["art_defaults"],
+
+    // Note that this tool needs to be built for both 32-bit and 64-bit since it requires
+    // to be same ISA as what it is attached to.
+    compile_multilib: "both",
+
+    header_libs: [
+        "libopenjdkjvmti_headers",
+        "libnativehelper_header_only",
+        "jni_headers",
+    ],
+    multilib: {
+        lib32: {
+            suffix: "32",
+        },
+        lib64: {
+            suffix: "64",
+        },
+    },
+    symlink_preferred_arch: true,
+}
+
+cc_defaults {
+    name: "chainagents-defaults",
+    host_supported: true,
+    shared_libs: [
+        "libbase",
+    ],
+    defaults: ["chainagents-base-defaults"],
+}
+
+art_cc_library {
+    name: "libchainagents",
+    defaults: ["chainagents-defaults"],
+}
+
+art_cc_library {
+    name: "libchainagentsd",
+    defaults: [
+        "art_debug_defaults",
+        "chainagents-defaults",
+    ],
+}
+
+cc_defaults {
+    name: "chainagents-static-defaults",
+    host_supported: false,
+    defaults: ["chainagents-base-defaults"],
+
+    shared_libs: [
+        "liblog",
+    ],
+    static_libs: [
+        "libbase_ndk",
+    ],
+    sdk_version: "current",
+    stl: "c++_static",
+}
+
+cc_library {
+    name: "libchainagentss",
+    defaults: ["chainagents-static-defaults"],
+}