ART: IRT refactor

IRT creation might fail. Add a path that allows to bypass the aborts
and instead signal validity. Hide this path with a private constructor,
rewrite users to use a static Create method.

Bug: 20110201

Change-Id: I440499c3372cd7557eb970b70ce2c4543da520e4
diff --git a/runtime/jni_env_ext.h b/runtime/jni_env_ext.h
index af87cb4..29d912c 100644
--- a/runtime/jni_env_ext.h
+++ b/runtime/jni_env_ext.h
@@ -34,7 +34,8 @@
 static constexpr size_t kLocalsMax = 512;
 
 struct JNIEnvExt : public JNIEnv {
-  JNIEnvExt(Thread* self, JavaVMExt* vm);
+  static JNIEnvExt* Create(Thread* self, JavaVMExt* vm);
+
   ~JNIEnvExt();
 
   void DumpReferenceTables(std::ostream& os)
@@ -87,6 +88,11 @@
 
   // Used by -Xcheck:jni.
   const JNINativeInterface* unchecked_functions;
+
+ private:
+  // The constructor should not be called directly. It may leave the object in an erronuous state,
+  // and the result needs to be checked.
+  JNIEnvExt(Thread* self, JavaVMExt* vm);
 };
 
 // Used to save and restore the JNIEnvExt state when not going through code created by the JNI