Use ScopedArenaAllocator for building HGraph.

Memory needed to compile the two most expensive methods for
aosp_angler-userdebug boot image:
  BatteryStats.dumpCheckinLocked() : 21.1MiB -> 20.2MiB
  BatteryStats.dumpLocked(): 42.0MiB -> 40.3MiB
This is because all the memory previously used by the graph
builder is reused by later passes.

And finish the "arena"->"allocator" renaming; make renamed
allocator pointers that are members of classes const when
appropriate (and make a few more members around them const).

Test: m test-art-host-gtest
Test: testrunner.py --host
Bug: 64312607
Change-Id: Ia50aafc80c05941ae5b96984ba4f31ed4c78255e
diff --git a/compiler/optimizing/scheduler.cc b/compiler/optimizing/scheduler.cc
index c673d54..57eb762 100644
--- a/compiler/optimizing/scheduler.cc
+++ b/compiler/optimizing/scheduler.cc
@@ -781,7 +781,7 @@
 #if defined(ART_ENABLE_CODEGEN_arm64) || defined(ART_ENABLE_CODEGEN_arm)
   // Phase-local allocator that allocates scheduler internal data structures like
   // scheduling nodes, internel nodes map, dependencies, etc.
-  ScopedArenaAllocator arena_allocator(graph_->GetArenaStack());
+  ScopedArenaAllocator allocator(graph_->GetArenaStack());
   CriticalPathSchedulingNodeSelector critical_path_selector;
   RandomSchedulingNodeSelector random_selector;
   SchedulingNodeSelector* selector = schedule_randomly
@@ -797,7 +797,7 @@
   switch (instruction_set_) {
 #ifdef ART_ENABLE_CODEGEN_arm64
     case kArm64: {
-      arm64::HSchedulerARM64 scheduler(&arena_allocator, selector);
+      arm64::HSchedulerARM64 scheduler(&allocator, selector);
       scheduler.SetOnlyOptimizeLoopBlocks(only_optimize_loop_blocks);
       scheduler.Schedule(graph_);
       break;
@@ -807,7 +807,7 @@
     case kThumb2:
     case kArm: {
       arm::SchedulingLatencyVisitorARM arm_latency_visitor(codegen_);
-      arm::HSchedulerARM scheduler(&arena_allocator, selector, &arm_latency_visitor);
+      arm::HSchedulerARM scheduler(&allocator, selector, &arm_latency_visitor);
       scheduler.SetOnlyOptimizeLoopBlocks(only_optimize_loop_blocks);
       scheduler.Schedule(graph_);
       break;