Make arm assembler explicitly take both registers for load/store-pair.

runtime/vm/assembler_arm.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ASSEMBLER_ARM_H_
 #define VM_ASSEMBLER_ARM_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_arm.h directly; use assembler.h instead.
 #endif
@@ skipping 495 matching lines @@
 
   void ldrh(Register rd, Address ad, Condition cond = AL);
   void strh(Register rd, Address ad, Condition cond = AL);
 
   void ldrsb(Register rd, Address ad, Condition cond = AL);
   void ldrsh(Register rd, Address ad, Condition cond = AL);
 
   // ldrd and strd actually support the full range of addressing modes, but
   // we don't use them, and we need to split them up into two instructions for
   // ARMv5TE, so we only support the base + offset mode.
-  void ldrd(Register rd, Register rn, int32_t offset, Condition cond = AL);
-  void strd(Register rd, Register rn, int32_t offset, Condition cond = AL);
+  // rd must be an even register and rd2 must be rd + 1.
+  void ldrd(Register rd, Register rd2, Register rn, int32_t offset,
+            Condition cond = AL);
+  void strd(Register rd, Register rd2, Register rn, int32_t offset,
+            Condition cond = AL);
 
   void ldm(BlockAddressMode am, Register base,
            RegList regs, Condition cond = AL);
   void stm(BlockAddressMode am, Register base,
            RegList regs, Condition cond = AL);
 
   void ldrex(Register rd, Register rn, Condition cond = AL);
   void strex(Register rd, Register rt, Register rn, Condition cond = AL);
 
   // Miscellaneous instructions.
@@ skipping 673 matching lines @@
                      Register new_value,
                      FieldContent old_content);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_ARM_H_