Clean up optimizing compiler stats

- removed unused stats.
- add 'OptStat' prefix to the names of the printed
stats to make them `grep` friendly.

Change-Id: I189e98b5226465c88c4a00247cd0b9b2ddb6d66e
diff --git a/compiler/optimizing/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index 2204921..c95aeeb 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -598,8 +598,6 @@
   stack_map.resize(codegen->ComputeStackMapsSize());
   codegen->BuildStackMaps(MemoryRegion(stack_map.data(), stack_map.size()));
 
-  MaybeRecordStat(MethodCompilationStat::kCompiledOptimized);
-
   CompiledMethod* compiled_method = CompiledMethod::SwapAllocCompiledMethod(
       compiler_driver,
       codegen->GetInstructionSet(),
@@ -634,7 +632,6 @@
   ArenaVector<uint8_t> gc_map(arena->Adapter(kArenaAllocBaselineMaps));
   codegen->BuildNativeGCMap(&gc_map, *compiler_driver);
 
-  MaybeRecordStat(MethodCompilationStat::kCompiledBaseline);
   CompiledMethod* compiled_method = CompiledMethod::SwapAllocCompiledMethod(
       compiler_driver,
       codegen->GetInstructionSet(),
@@ -839,6 +836,7 @@
                    dex_file,
                    dex_cache));
     if (codegen.get() != nullptr) {
+      MaybeRecordStat(MethodCompilationStat::kCompiled);
       if (run_optimizations_) {
         method = EmitOptimized(&arena, &code_allocator, codegen.get(), compiler_driver);
       } else {
@@ -849,7 +847,7 @@
     if (compiler_driver->GetCompilerOptions().VerifyAtRuntime()) {
       MaybeRecordStat(MethodCompilationStat::kNotCompiledVerifyAtRuntime);
     } else {
-      MaybeRecordStat(MethodCompilationStat::kNotCompiledClassNotVerified);
+      MaybeRecordStat(MethodCompilationStat::kNotCompiledVerificationError);
     }
   }