Make ScopedAssertNoThreadSuspension no overhead for non-debug

Previously it required Thread::Current() which may not be free.
The plan is to add a lot more ScopedAssertNoThreadSuspension in
the codebase.

Also cleaned up callers.

Bug: 31458474
Change-Id: I5a1621a5435476504d22266cc01a9bf26aab7568
diff --git a/runtime/debugger.cc b/runtime/debugger.cc
index 9f3c2aa..2821004 100644
--- a/runtime/debugger.cc
+++ b/runtime/debugger.cc
@@ -1986,7 +1986,7 @@
   if (error != JDWP::ERR_NONE) {
     return JDWP::ERR_INVALID_OBJECT;
   }
-  ScopedAssertNoThreadSuspension ants(soa.Self(), "Debugger: GetThreadGroup");
+  ScopedAssertNoThreadSuspension ants("Debugger: GetThreadGroup");
   // Okay, so it's an object, but is it actually a thread?
   DecodeThread(soa, thread_id, &error);
   if (error == JDWP::ERR_THREAD_NOT_ALIVE) {
@@ -2036,7 +2036,7 @@
   if (error != JDWP::ERR_NONE) {
     return error;
   }
-  ScopedAssertNoThreadSuspension ants(soa.Self(), "Debugger: GetThreadGroupName");
+  ScopedAssertNoThreadSuspension ants("Debugger: GetThreadGroupName");
   ArtField* f = soa.DecodeField(WellKnownClasses::java_lang_ThreadGroup_name);
   CHECK(f != nullptr);
   mirror::String* s = reinterpret_cast<mirror::String*>(f->GetObject(thread_group));
@@ -2055,7 +2055,7 @@
   }
   mirror::Object* parent;
   {
-    ScopedAssertNoThreadSuspension ants(soa.Self(), "Debugger: GetThreadGroupParent");
+    ScopedAssertNoThreadSuspension ants("Debugger: GetThreadGroupParent");
     ArtField* f = soa.DecodeField(WellKnownClasses::java_lang_ThreadGroup_parent);
     CHECK(f != nullptr);
     parent = f->GetObject(thread_group);