Avoid std::string allocations for finding an array class.

Introduce ClassLinker::FindArrayClass which performs an array class lookup
given the element/component class. This has a 16 element cache of recently
looked up arrays.
Pass the current thread to ClassLinker Find .. Class routines to avoid calls
to Thread::Current().
Avoid some uses of FindClass in the debugger where WellKnownClasses is a
faster and more compacting GC friendly alternative.

Change-Id: I60e231820b349543a7edb3ceb9cf1ce92db3c843
diff --git a/runtime/indirect_reference_table_test.cc b/runtime/indirect_reference_table_test.cc
index b6c6cb4..78e1992 100644
--- a/runtime/indirect_reference_table_test.cc
+++ b/runtime/indirect_reference_table_test.cc
@@ -48,7 +48,7 @@
   static const size_t kTableMax = 20;
   IndirectReferenceTable irt(kTableInitial, kTableMax, kGlobal);
 
-  mirror::Class* c = class_linker_->FindSystemClass("Ljava/lang/Object;");
+  mirror::Class* c = class_linker_->FindSystemClass(soa.Self(), "Ljava/lang/Object;");
   ASSERT_TRUE(c != NULL);
   mirror::Object* obj0 = c->AllocObject(soa.Self());
   ASSERT_TRUE(obj0 != NULL);