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/utils_test.cc b/runtime/utils_test.cc
index b43177b..150695b 100644
--- a/runtime/utils_test.cc
+++ b/runtime/utils_test.cc
@@ -99,7 +99,7 @@
   SirtRef<mirror::ShortArray> a(soa.Self(), mirror::ShortArray::Alloc(soa.Self(), 2));
   EXPECT_EQ("short[]", PrettyTypeOf(a.get()));
 
-  mirror::Class* c = class_linker_->FindSystemClass("[Ljava/lang/String;");
+  mirror::Class* c = class_linker_->FindSystemClass(soa.Self(), "[Ljava/lang/String;");
   ASSERT_TRUE(c != NULL);
   mirror::Object* o = mirror::ObjectArray<mirror::String>::Alloc(soa.Self(), c, 0);
   EXPECT_EQ("java.lang.String[]", PrettyTypeOf(o));
@@ -109,7 +109,7 @@
 TEST_F(UtilsTest, PrettyClass) {
   ScopedObjectAccess soa(Thread::Current());
   EXPECT_EQ("null", PrettyClass(NULL));
-  mirror::Class* c = class_linker_->FindSystemClass("[Ljava/lang/String;");
+  mirror::Class* c = class_linker_->FindSystemClass(soa.Self(), "[Ljava/lang/String;");
   ASSERT_TRUE(c != NULL);
   mirror::Object* o = mirror::ObjectArray<mirror::String>::Alloc(soa.Self(), c, 0);
   EXPECT_EQ("java.lang.Class<java.lang.String[]>", PrettyClass(o->GetClass()));
@@ -118,7 +118,7 @@
 TEST_F(UtilsTest, PrettyClassAndClassLoader) {
   ScopedObjectAccess soa(Thread::Current());
   EXPECT_EQ("null", PrettyClassAndClassLoader(NULL));
-  mirror::Class* c = class_linker_->FindSystemClass("[Ljava/lang/String;");
+  mirror::Class* c = class_linker_->FindSystemClass(soa.Self(), "[Ljava/lang/String;");
   ASSERT_TRUE(c != NULL);
   mirror::Object* o = mirror::ObjectArray<mirror::String>::Alloc(soa.Self(), c, 0);
   EXPECT_EQ("java.lang.Class<java.lang.String[],null>", PrettyClassAndClassLoader(o->GetClass()));
@@ -128,7 +128,8 @@
   ScopedObjectAccess soa(Thread::Current());
   EXPECT_EQ("null", PrettyField(NULL));
 
-  mirror::Class* java_lang_String = class_linker_->FindSystemClass("Ljava/lang/String;");
+  mirror::Class* java_lang_String = class_linker_->FindSystemClass(soa.Self(),
+                                                                   "Ljava/lang/String;");
 
   mirror::ArtField* f;
   f = java_lang_String->FindDeclaredInstanceField("count", "I");
@@ -197,7 +198,7 @@
 
 TEST_F(UtilsTest, JniShortName_JniLongName) {
   ScopedObjectAccess soa(Thread::Current());
-  mirror::Class* c = class_linker_->FindSystemClass("Ljava/lang/String;");
+  mirror::Class* c = class_linker_->FindSystemClass(soa.Self(), "Ljava/lang/String;");
   ASSERT_TRUE(c != NULL);
   mirror::ArtMethod* m;