Fix some more shorten-64-to-32 warnings:

runtime/vm/deopt_instructions.cc

Index: runtime/vm/deopt_instructions.cc
diff --git a/runtime/vm/deopt_instructions.cc b/runtime/vm/deopt_instructions.cc
index 5d985a323703a97a2515281d5ba601a7324b2df5..bdb503509282b7a44cfbde7b4c52ebc59de736a0 100644
--- a/runtime/vm/deopt_instructions.cc
+++ b/runtime/vm/deopt_instructions.cc
@@ -423,8 +423,10 @@ class DeoptRetAddressInstr : public DeoptInstr {
 
  private:
   static const intptr_t kFieldWidth = kBitsPerWord / 2;
-  class ObjectTableIndex : public BitField<intptr_t, 0, kFieldWidth> { };
-  class DeoptId : public BitField<intptr_t, kFieldWidth, kFieldWidth> { };
+  class ObjectTableIndex :
+      public BitField<intptr_t, intptr_t, 0, kFieldWidth> { };
+  class DeoptId :
+      public BitField<intptr_t, intptr_t, kFieldWidth, kFieldWidth> { };
 
   const intptr_t object_table_index_;
   const intptr_t deopt_id_;
@@ -547,8 +549,9 @@ class DeoptMintPairInstr: public DeoptIntegerInstrBase {
 
  private:
   static const intptr_t kFieldWidth = kBitsPerWord / 2;
-  class LoRegister : public BitField<intptr_t, 0, kFieldWidth> { };
-  class HiRegister : public BitField<intptr_t, kFieldWidth, kFieldWidth> { };
+  class LoRegister : public BitField<intptr_t, intptr_t, 0, kFieldWidth> { };
+  class HiRegister :
+      public BitField<intptr_t, intptr_t, kFieldWidth, kFieldWidth> { };
 
   const CpuRegisterSource lo_;
   const CpuRegisterSource hi_;