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/mirror/art_method.h b/runtime/mirror/art_method.h
index 4ebceff..fa592c2 100644
--- a/runtime/mirror/art_method.h
+++ b/runtime/mirror/art_method.h
@@ -446,7 +446,7 @@
 
   const Signature GetSignature() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  const char* GetName() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  ALWAYS_INLINE const char* GetName() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   const DexFile::CodeItem* GetCodeItem() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
@@ -473,7 +473,7 @@
 
   mirror::DexCache* GetDexCache() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  ArtMethod* GetInterfaceMethodIfProxy() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  ALWAYS_INLINE ArtMethod* GetInterfaceMethodIfProxy() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
  protected:
   // Field order required by test "ValidateFieldOrderOfJavaCppUnionClasses".