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/interpreter/interpreter_common.cc b/runtime/interpreter/interpreter_common.cc
index 9e1d915..83a1fbc 100644
--- a/runtime/interpreter/interpreter_common.cc
+++ b/runtime/interpreter/interpreter_common.cc
@@ -280,7 +280,7 @@
     std::string descriptor(DotToDescriptor(shadow_frame->GetVRegReference(arg_offset)->AsString()->ToModifiedUtf8().c_str()));
 
     SirtRef<ClassLoader> class_loader(self, nullptr);  // shadow_frame.GetMethod()->GetDeclaringClass()->GetClassLoader();
-    Class* found = Runtime::Current()->GetClassLinker()->FindClass(descriptor.c_str(),
+    Class* found = Runtime::Current()->GetClassLinker()->FindClass(self, descriptor.c_str(),
                                                                    class_loader);
     CHECK(found != NULL) << "Class.forName failed in un-started runtime for class: "
         << PrettyDescriptor(descriptor);
@@ -289,7 +289,7 @@
     SirtRef<ClassLoader> class_loader(self, down_cast<mirror::ClassLoader*>(shadow_frame->GetVRegReference(arg_offset)));
     std::string descriptor(DotToDescriptor(shadow_frame->GetVRegReference(arg_offset + 1)->AsString()->ToModifiedUtf8().c_str()));
 
-    Class* found = Runtime::Current()->GetClassLinker()->FindClass(descriptor.c_str(),
+    Class* found = Runtime::Current()->GetClassLinker()->FindClass(self, descriptor.c_str(),
                                                                    class_loader);
     result->SetL(found);
   } else if (name == "java.lang.Object java.lang.Class.newInstance()") {