[heap] User safer root set accessor when possible.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 5e071d5e4c2dc923ca389664af4f6ceb7cee46d3..5d0347c56332328ff67e0041ffac372a58df1da4 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -425,7 +425,7 @@ void MacroAssembler::LoadRoot(Register destination,
       !predictable_code_size()) {
     // The CPU supports fast immediate values, and this root will never
     // change. We will load it as a relocatable immediate value.
-    Handle<Object> root(&isolate()->heap()->roots_array_start()[index]);
+    Handle<Object> root = isolate()->heap()->root_handle(index);
     mov(destination, Operand(root), LeaveCC, cond);
     return;
   }