Add list extensions agent

Add a small agent that just lists jvmti extensions.

Test: ./test/run-test --host --with-agent liblistextensions.so --dev 001-HelloWorld

Change-Id: I1335206c0a1dfc7ad311ec7ab5d75ee07df63957
diff --git a/tools/jvmti-agents/list-extensions/Android.bp b/tools/jvmti-agents/list-extensions/Android.bp
new file mode 100644
index 0000000..fcf883c
--- /dev/null
+++ b/tools/jvmti-agents/list-extensions/Android.bp
@@ -0,0 +1,56 @@
+//
+// 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: "listextensions-defaults",
+    host_supported: true,
+    srcs: ["list-extensions.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",
+
+    shared_libs: [
+        "libbase",
+    ],
+    header_libs: [
+        "libopenjdkjvmti_headers",
+    ],
+    multilib: {
+        lib32: {
+            suffix: "32",
+        },
+        lib64: {
+            suffix: "64",
+        },
+    },
+    symlink_preferred_arch: true,
+}
+
+art_cc_library {
+    name: "liblistextensions",
+    defaults: ["listextensions-defaults"],
+}
+
+art_cc_library {
+    name: "liblistextensionsd",
+    defaults: [
+        "art_debug_defaults",
+        "listextensions-defaults",
+    ],
+}