Remove default argument values in GenerateGcRootFieldLoad.

These values were never or rarely used.

Test: mmma art (with and without `ART_USE_READ_BARRIER=true`)
Bug: 12687968
Bug: 29516974
Change-Id: I5d15140ce501bf50d7a87871b1e492cee54913db
diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc
index cac0543..b9e049a 100644
--- a/compiler/optimizing/code_generator_arm_vixl.cc
+++ b/compiler/optimizing/code_generator_arm_vixl.cc
@@ -3357,7 +3357,8 @@
       GenerateGcRootFieldLoad(cls,
                               out_loc,
                               current_method,
-                              ArtMethod::DeclaringClassOffset().Int32Value());
+                              ArtMethod::DeclaringClassOffset().Int32Value(),
+                              kEmitCompilerReadBarrier);
       break;
     }
     case HLoadClass::LoadKind::kDexCacheViaMethod: {
@@ -3369,7 +3370,7 @@
       GetAssembler()->LoadFromOffset(kLoadWord, out, current_method, resolved_types_offset);
       // /* GcRoot<mirror::Class> */ out = out[type_index]
       size_t offset = CodeGenerator::GetCacheOffset(cls->GetTypeIndex());
-      GenerateGcRootFieldLoad(cls, out_loc, out, offset);
+      GenerateGcRootFieldLoad(cls, out_loc, out, offset, kEmitCompilerReadBarrier);
       generate_null_check = !cls->IsInDexCache();
       break;
     }