Avoid use of std::string where we have const char*.

Removing the ClassHelper caused std::string creation for all calls to
Class::GetDescriptor and a significant performance regression. Make the
std::string an out argument so the caller can maintain it and its life time
while allowing GetDescriptor to return the common const char* case.

Don't generate GC maps when compilation is disabled.

Remove other uses of std::string that are occuring on critical paths.
Use the cheaper SkipClass in CompileMethod in CompilerDriver.
Specialize the utf8 as utf16 comparison code for the common shorter byte
encoding.
Force a bit of inlining, remove some UNLIKELYs (they are prone to pessimizing
code), add some LIKELYs.

x86-64 host 1-thread interpret-only of 57 apks:
Before: 29.539s
After: 23.467s

Regular compile:
Before: 1m35.347s
After: 1m20.056s

Bug: 16853450
Change-Id: Ic705ea24784bee24ab80084d06174cbf87d557ad
diff --git a/runtime/native/java_lang_reflect_Array.cc b/runtime/native/java_lang_reflect_Array.cc
index f94e42b..058458f 100644
--- a/runtime/native/java_lang_reflect_Array.cc
+++ b/runtime/native/java_lang_reflect_Array.cc
@@ -34,7 +34,8 @@
   DCHECK(javaDimArray != NULL);
   mirror::Object* dimensions_obj = soa.Decode<mirror::Object*>(javaDimArray);
   DCHECK(dimensions_obj->IsArrayInstance());
-  DCHECK_STREQ(dimensions_obj->GetClass()->GetDescriptor().c_str(), "[I");
+  DCHECK_EQ(dimensions_obj->GetClass()->GetComponentType()->GetPrimitiveType(),
+            Primitive::kPrimInt);
   Handle<mirror::IntArray> dimensions_array(
       hs.NewHandle(down_cast<mirror::IntArray*>(dimensions_obj)));
   mirror::Array* new_array = mirror::Array::CreateMultiArray(soa.Self(), element_class,