ART: Wire up DexToDexCompiler without extern

The extern declaration actually had the wrong signature, a parameter
was missing, and we never noticed.

Remove the function field and extern. Add a header for the compiler.
Use the header file.

Change-Id: Ia4d4dd86211da6045709a45c7bf8430471d1b62b
diff --git a/compiler/dex/dex_to_dex_compiler.h b/compiler/dex/dex_to_dex_compiler.h
new file mode 100644
index 0000000..3fad6d4
--- /dev/null
+++ b/compiler/dex/dex_to_dex_compiler.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2015 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 ART_COMPILER_DEX_DEX_TO_DEX_COMPILER_H_
+#define ART_COMPILER_DEX_DEX_TO_DEX_COMPILER_H_
+
+#include "jni.h"
+
+#include "dex_file.h"
+#include "invoke_type.h"
+
+namespace art {
+
+class CompiledMethod;
+class CompilerDriver;
+
+namespace optimizer {
+
+enum class DexToDexCompilationLevel {
+  kDontDexToDexCompile,   // Only meaning wrt image time interpretation.
+  kRequired,              // Dex-to-dex compilation required for correctness.
+  kOptimize               // Perform required transformation and peep-hole optimizations.
+};
+std::ostream& operator<<(std::ostream& os, const DexToDexCompilationLevel& rhs);
+
+CompiledMethod* ArtCompileDEX(CompilerDriver* driver,
+                              const DexFile::CodeItem* code_item,
+                              uint32_t access_flags,
+                              InvokeType invoke_type,
+                              uint16_t class_def_idx,
+                              uint32_t method_idx,
+                              jobject class_loader,
+                              const DexFile& dex_file,
+                              DexToDexCompilationLevel dex_to_dex_compilation_level);
+
+}  // namespace optimizer
+
+}  // namespace art
+
+#endif  // ART_COMPILER_DEX_DEX_TO_DEX_COMPILER_H_