[metrics] Add ClassLoadingTotalTime counter

This keeps track of how much time we spend in the class loading
process.

Testing instructions:

   adb shell setprop dalvik.vm.metrics.write-to-log true
   adb shell stop && adb shell start
   adb logcat -e "ART internal metrics"

Observer ClassLoadingTotalTime in internal metrics report. Example:

    *** ART internal metrics ***
      Metadata:
        timestamp_since_start_ms: 34555
        session_id: 2710488913234081424
        uid: 10065
        compilation_reason: Unknown
        compiler_filter: (unspecified)
      Metrics:
        ClassLoadingTotalTime: count = 120959
        ClassVerificationTotalTime: count = 216121
        JitMethodCompileTime: range = 0...1000000, buckets: 4482,10,2,3
    *** Done dumping ART internal metrics ***

Bug: 177591870
Test: Manual, see above
Change-Id: I24f0c94ab6af5e6cd9b0dc32122f2905c36cf3b7
diff --git a/libartbase/base/metrics/metrics_test.cc b/libartbase/base/metrics/metrics_test.cc
index 4643f14..44a3b60 100644
--- a/libartbase/base/metrics/metrics_test.cc
+++ b/libartbase/base/metrics/metrics_test.cc
@@ -215,13 +215,13 @@
   // Make sure the resulting string lists all the counters.
   const std::string result = backend.GetAndResetBuffer();
 #define COUNTER(name) \
-  EXPECT_NE(result.find(DatumName(DatumId::k##name)), std::string::npos)
+  EXPECT_NE(result.find(DatumName(DatumId::k##name)), std::string::npos);
   ART_COUNTERS(COUNTER);
 #undef COUNTER
 
   // Make sure the resulting string lists all the histograms.
 #define HISTOGRAM(name, num_buckets, minimum_value, maximum_value) \
-  EXPECT_NE(result.find(DatumName(DatumId::k##name)), std::string::npos)
+  EXPECT_NE(result.find(DatumName(DatumId::k##name)), std::string::npos);
   ART_HISTOGRAMS(HISTOGRAM);
 #undef HISTOGRAM
 }