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/interpreter/interpreter_goto_table_impl.cc b/runtime/interpreter/interpreter_goto_table_impl.cc
index abd4b44..e098ac8 100644
--- a/runtime/interpreter/interpreter_goto_table_impl.cc
+++ b/runtime/interpreter/interpreter_goto_table_impl.cc
@@ -341,11 +341,12 @@
       }
       if (!obj_result->VerifierInstanceOf(return_type)) {
         // This should never happen.
+        std::string temp1, temp2;
         self->ThrowNewExceptionF(self->GetCurrentLocationForThrow(),
                                  "Ljava/lang/VirtualMachineError;",
                                  "Returning '%s' that is not instance of return type '%s'",
-                                 obj_result->GetClass()->GetDescriptor().c_str(),
-                                 return_type->GetDescriptor().c_str());
+                                 obj_result->GetClass()->GetDescriptor(&temp1),
+                                 return_type->GetDescriptor(&temp2));
         HANDLE_PENDING_EXCEPTION();
       }
     }
@@ -615,10 +616,11 @@
       ThrowNullPointerException(NULL, "throw with null exception");
     } else if (do_assignability_check && !exception->GetClass()->IsThrowableClass()) {
       // This should never happen.
+      std::string temp;
       self->ThrowNewExceptionF(self->GetCurrentLocationForThrow(),
                                "Ljava/lang/VirtualMachineError;",
                                "Throwing '%s' that is not instance of Throwable",
-                               exception->GetClass()->GetDescriptor().c_str());
+                               exception->GetClass()->GetDescriptor(&temp));
     } else {
       self->SetException(shadow_frame.GetCurrentLocationForThrow(), exception->AsThrowable());
     }