installd: Unit test for RunDex2oat

Add unit tests run_dex2oat_test.

In order to make RunDex2oat testable,
 - RunDex2Oat is extracted from dexopt.cpp such that the class is
   visible to test
 - ExecVHelper is extracted from dexopt.cpp such that it can be used by
   RunDex2Oat and the others in the original file.
 - Main logic of RunDex2Oat is removed from constructor (otherwise
   virtual functions can't be overridden in derived class).

Bug: 161470356
Test: atest run_dex2oat_test
Test: atest frameworks/native/cmds/installd/tests
Test: cmd package compile -m speed -f com.android.egg

Change-Id: I416d57a008374a598def9160b65407ed043ab0eb
diff --git a/cmds/installd/execv_helper.h b/cmds/installd/execv_helper.h
new file mode 100644
index 0000000..9adfc0e
--- /dev/null
+++ b/cmds/installd/execv_helper.h
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#ifndef ANDROID_INSTALLD_EXECV_HELPER_H
+#define ANDROID_INSTALLD_EXECV_HELPER_H
+
+#include <string>
+#include <vector>
+
+namespace android {
+namespace installd {
+
+// ExecVHelper prepares and holds pointers to parsed command line arguments so that no allocations
+// need to be performed between the fork and exec.
+class ExecVHelper {
+  public:
+    ExecVHelper();
+    virtual ~ExecVHelper();
+
+    [[ noreturn ]]
+    virtual void Exec(int exit_code);
+
+    void PrepareArgs(const std::string& bin);
+
+    // Add an arg if it's not empty.
+    void AddArg(const std::string& arg);
+
+    // Add a runtime arg if it's not empty.
+    void AddRuntimeArg(const std::string& arg);
+
+  protected:
+    // Holder arrays for backing arg storage.
+    std::vector<std::string> args_;
+
+    // Argument poiners.
+    std::vector<const char*> argv_;
+};
+
+}  // namespace installd
+}  // namespace android
+
+#endif  // ANDROID_INSTALLD_EXECV_HELPER_H