Reuse HUseListNode<>s when replacing instruction or input.

Compiling the Nexus 5 boot image with the 64-bit dex2oat
on host this CL reduces the memory used for compiling the
most hungry method, BatteryStats.dumpLocked(), by ~5.6MiB:

Before:
  MEM: used: 44393040, allocated: 45361248, lost: 968208
  Number of arenas allocated: 319,
  Number of allocations: 815492, avg size: 54
  ...
  UseListNode    10308480
  ...
After:
  MEM: used: 38554536, allocated: 39463008, lost: 908472
  Number of arenas allocated: 274,
  Number of allocations: 572221, avg size: 67
  ...
  UseListNode     4469976
  ...

With 32-bit dex2oat, the UseListNode would be 2/3 of the
values for 64-bit dex2oat (both before and after).

Bug: 28173563
Change-Id: Ia4fabe03568f0e0dbf2cdf2b031863602aea3530
diff --git a/compiler/optimizing/ssa_test.cc b/compiler/optimizing/ssa_test.cc
index 218bd53..4297634 100644
--- a/compiler/optimizing/ssa_test.cc
+++ b/compiler/optimizing/ssa_test.cc
@@ -346,7 +346,7 @@
     "BasicBlock 7, pred: 6\n"
     "  12: Exit\n"
     "BasicBlock 8, pred: 2, 3, succ: 4\n"
-    "  13: Phi(2, 1) [8, 8, 11]\n"
+    "  13: Phi(2, 1) [11, 8, 8]\n"
     "  14: Goto\n";
 
   const uint16_t data[] = ONE_REGISTER_CODE_ITEM(