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/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index 9bfb7a5..42f32b7 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -1146,7 +1146,8 @@
         if (total_allocated > kArenaAllocatorMemoryReportThreshold) {
           MemStats mem_stats(allocator.GetMemStats());
           MemStats peak_stats(arena_stack.GetPeakStats());
-          LOG(INFO) << dex_file.PrettyMethod(method_idx)
+          LOG(INFO) << "Used " << total_allocated << " bytes of arena memory for compiling "
+                    << dex_file.PrettyMethod(method_idx)
                     << "\n" << Dumpable<MemStats>(mem_stats)
                     << "\n" << Dumpable<MemStats>(peak_stats);
         }
@@ -1256,7 +1257,8 @@
       if (total_allocated > kArenaAllocatorMemoryReportThreshold) {
         MemStats mem_stats(allocator.GetMemStats());
         MemStats peak_stats(arena_stack.GetPeakStats());
-        LOG(INFO) << dex_file->PrettyMethod(method_idx)
+        LOG(INFO) << "Used " << total_allocated << " bytes of arena memory for compiling "
+                  << dex_file->PrettyMethod(method_idx)
                   << "\n" << Dumpable<MemStats>(mem_stats)
                   << "\n" << Dumpable<MemStats>(peak_stats);
       }