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/verifier/reg_type.cc b/runtime/verifier/reg_type.cc
index 6422cdf..30be82f 100644
--- a/runtime/verifier/reg_type.cc
+++ b/runtime/verifier/reg_type.cc
@@ -414,20 +414,22 @@
 
 std::string UnresolvedReferenceType::Dump() {
   std::stringstream result;
-  result << "Unresolved Reference" << ": " << PrettyDescriptor(GetDescriptor());
+  result << "Unresolved Reference" << ": " << PrettyDescriptor(GetDescriptor().c_str());
   return result.str();
 }
 
 std::string UnresolvedUninitializedRefType::Dump() {
   std::stringstream result;
-  result << "Unresolved And Uninitialized Reference" << ": " << PrettyDescriptor(GetDescriptor());
-  result << " Allocation PC: " << GetAllocationPc();
+  result << "Unresolved And Uninitialized Reference" << ": "
+      << PrettyDescriptor(GetDescriptor().c_str())
+      << " Allocation PC: " << GetAllocationPc();
   return result.str();
 }
 
 std::string UnresolvedUninitializedThisRefType::Dump() {
   std::stringstream result;
-  result << "Unresolved And Uninitialized This Reference" << PrettyDescriptor(GetDescriptor());
+  result << "Unresolved And Uninitialized This Reference"
+      << PrettyDescriptor(GetDescriptor().c_str());
   return result.str();
 }
 
@@ -618,7 +620,8 @@
     if (super_klass != NULL) {
       // A super class of a precise type isn't precise as a precise type indicates the register
       // holds exactly that type.
-      return cache->FromClass(super_klass->GetDescriptor().c_str(), super_klass, false);
+      std::string temp;
+      return cache->FromClass(super_klass->GetDescriptor(&temp), super_klass, false);
     } else {
       return cache->Zero();
     }
@@ -896,7 +899,8 @@
       } else if (c2 == join_class && !incoming_type.IsPreciseReference()) {
         return incoming_type;
       } else {
-        return reg_types->FromClass(join_class->GetDescriptor().c_str(), join_class, false);
+        std::string temp;
+        return reg_types->FromClass(join_class->GetDescriptor(&temp), join_class, false);
       }
     }
   } else {