Fix x86 & x86-64 UnsafeGetObject intrinsics with read barriers.

The implementation was incorrectly interpreting the 'offset'
input as an index in a (4-byte) object reference array,
whereas it is a (1-byte) offset to an object reference field
within the 'base' (object) input.

Bug: 29516905
Change-Id: Idfbead8289222b55069816a81284401eff791e85
Test: Covered by test/004-UnsafeTest.
diff --git a/compiler/optimizing/code_generator_x86.h b/compiler/optimizing/code_generator_x86.h
index 98dc8ca..1a01df9 100644
--- a/compiler/optimizing/code_generator_x86.h
+++ b/compiler/optimizing/code_generator_x86.h
@@ -485,6 +485,14 @@
                                              Location index,
                                              Location temp,
                                              bool needs_null_check);
+  // Factored implementation used by GenerateFieldLoadWithBakerReadBarrier
+  // and GenerateArrayLoadWithBakerReadBarrier.
+  void GenerateReferenceLoadWithBakerReadBarrier(HInstruction* instruction,
+                                                 Location ref,
+                                                 Register obj,
+                                                 const Address& src,
+                                                 Location temp,
+                                                 bool needs_null_check);
 
   // Generate a read barrier for a heap reference within `instruction`
   // using a slow path.
@@ -555,15 +563,6 @@
   static constexpr int32_t kDummy32BitOffset = 256;
 
  private:
-  // Factored implementation of GenerateFieldLoadWithBakerReadBarrier
-  // and GenerateArrayLoadWithBakerReadBarrier.
-  void GenerateReferenceLoadWithBakerReadBarrier(HInstruction* instruction,
-                                                 Location ref,
-                                                 Register obj,
-                                                 const Address& src,
-                                                 Location temp,
-                                                 bool needs_null_check);
-
   Register GetInvokeStaticOrDirectExtraParameter(HInvokeStaticOrDirect* invoke, Register temp);
 
   struct PcRelativeDexCacheAccessInfo {