Give the JIT its own arena pool to avoid lock contentions.

Sharing it with the verifier and the class loader is not ideal,
especially at startup time.

bug:27398183
bug:23128949
Change-Id: I1b91663a13f6c5b33ad3b4be780d93eb7fe445b4
diff --git a/compiler/optimizing/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index 5a9f258..13d6d62 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -861,7 +861,7 @@
   const uint32_t access_flags = method->GetAccessFlags();
   const InvokeType invoke_type = method->GetInvokeType();
 
-  ArenaAllocator arena(Runtime::Current()->GetArenaPool());
+  ArenaAllocator arena(Runtime::Current()->GetJitArenaPool());
   CodeVectorAllocator code_allocator(&arena);
   std::unique_ptr<CodeGenerator> codegen;
   {