Change MemMap::maps_ to not be global variable

Runtime.exit() was causing globals to get destructed at the same time
that another thread was using it for allocating a new mem map.

Bug: 17962201
Change-Id: I400cb7b8141d858f3c08a6fe59a02838c04c6962
diff --git a/runtime/common_runtime_test.cc b/runtime/common_runtime_test.cc
index eed6f71..ea3da64 100644
--- a/runtime/common_runtime_test.cc
+++ b/runtime/common_runtime_test.cc
@@ -185,6 +185,8 @@
   int mkdir_result = mkdir(dalvik_cache_.c_str(), 0700);
   ASSERT_EQ(mkdir_result, 0);
 
+  MemMap::Init();  // For LoadExpectSingleDexFile
+
   std::string error_msg;
   java_lang_dex_file_ = LoadExpectSingleDexFile(GetLibCoreDexFileName().c_str());
   boot_class_path_.push_back(java_lang_dex_file_);