Fixes widevine metrics proto serialization

Changes to a much more efficient and more reusable protobuf format for
metrics.

Test: Widevine tests, Google Play and MediaDrm CTS test.
Bug: 73724218

Change-Id: I3299051d7a16bcd7758c8f272415ca40e10c1313

libwvdrmengine/cdm/metrics/include/pow2bucket.h

@@ -0,0 +1,50 @@
+// Copyright 2018 Google Inc. All Rights Reserved.
+//
+// This file contains the declaration of the Pow2Bucket class which
+// is a convenient way to bucketize sampled values into powers of 2.
+#ifndef WVCDM_METRICS_POW2BUCKET_H_
+#define WVCDM_METRICS_POW2BUCKET_H_
+
+namespace wvcdm {
+namespace metrics {
+
+// This class converts the size_t value into the highest power of two
+// below the value.  E.g. for 7, the value is 4.  For 11, the value is 8.
+// This class is intended to simplify the use of EventMetric Fields that may
+// have many possible values, but we want to bucket them into a small set of
+// numbers (32 or 64).
+class Pow2Bucket {
+ public:
+  explicit Pow2Bucket(size_t value) : value_(GetLowerBucket(value)) {}
+
+  Pow2Bucket(const Pow2Bucket &value) : value_(value.value_) {}
+
+  size_t value() const { return value_; }
+
+  // Support for converting to string.
+  friend std::ostream &operator<<(std::ostream &os, const Pow2Bucket &log) {
+    return os << log.value_;
+  }
+
+ private:
+  inline size_t GetLowerBucket(size_t value) {
+    if (!value) {
+      return 0;
+    }
+
+    size_t log = 0;
+    while (value) {
+      log++;
+      value >>= 1;
+    }
+
+    return 1u << (log - 1);
+  }
+
+  size_t value_;
+};
+
+}  // namespace metrics
+}  // namespace wvcdm
+
+#endif  // WVCDM_METRICS_POW2BUCKET_H_