Revert "Revert "Add one LinearAlloc per ClassLoader""

Issue was fixed by:
https://android-review.googlesource.com/#/c/171945/

Bug: 22720414

This reverts commit 7de5dfe37f3cf24e1166412b589f6f67dcd1f1c0.
diff --git a/runtime/class_linker_test.cc b/runtime/class_linker_test.cc
index b4ea3b3..0926ce3 100644
--- a/runtime/class_linker_test.cc
+++ b/runtime/class_linker_test.cc
@@ -550,6 +550,7 @@
 
 struct ClassLoaderOffsets : public CheckOffsets<mirror::ClassLoader> {
   ClassLoaderOffsets() : CheckOffsets<mirror::ClassLoader>(false, "Ljava/lang/ClassLoader;") {
+    addOffset(OFFSETOF_MEMBER(mirror::ClassLoader, allocator_), "allocator");
     addOffset(OFFSETOF_MEMBER(mirror::ClassLoader, class_table_), "classTable");
     addOffset(OFFSETOF_MEMBER(mirror::ClassLoader, packages_), "packages");
     addOffset(OFFSETOF_MEMBER(mirror::ClassLoader, parent_), "parent");