ARM/AOT: Allow 16-bit LDR for Baker read barrier loads.

Test: m test-art-target-gtest
Test: testrunner.py --target on Nexus 6P.
Test: testrunner.py --target on Nexus 6P with heap poisoning enabled.
Test: Repeat the above tests with ART_USE_OLD_ARM_BACKEND=true.
Bug: 29516974
Bug: 30126666
Bug: 36141117
Change-Id: I458f2ec5fe9abead4db06c7595d992945096fb68
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index ed0a64c..54aa03c 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -6094,7 +6094,7 @@
     //   not_gray_return_address:
     //     // Original reference load. If the offset is too large to fit
     //     // into LDR, we use an adjusted base register here.
-    //     GcRoot<mirror::Object> reference = *(obj+offset);
+    //     HeapReference<mirror::Object> reference = *(obj+offset);
     //   gray_return_address:
 
     DCHECK_ALIGNED(offset, sizeof(mirror::HeapReference<mirror::Object>));
@@ -6189,7 +6189,7 @@
     //   not_gray_return_address:
     //     // Original reference load. If the offset is too large to fit
     //     // into LDR, we use an adjusted base register here.
-    //     GcRoot<mirror::Object> reference = data[index];
+    //     HeapReference<mirror::Object> reference = data[index];
     //   gray_return_address:
 
     DCHECK(index.IsValid());