MediaMetrics: Add Defer class

This is a helper which assists logging on exit of a method.

Test: atest mediametrics_tests
Bug: 138583596
Change-Id: I73c0e7e469dc9fd1b29934ef308f9d2f15146bec

media/libmediametrics/include/MediaMetricsItem.h

@@ -131,6 +131,25 @@ static inline bool startsWith(const std::string &s, const char (&comp)[N]) {
     return !strncmp(s.c_str(), comp, N - 1);
 }
 
+static inline bool startsWith(const std::string& s, const std::string& comp) {
+    return !strncmp(s.c_str(), comp.c_str(), comp.size() - 1);
+}
+
+/**
+ * Defers a function to run in the destructor.
+ *
+ * This helper class is used to log results on exit of a method.
+ */
+class Defer {
+public:
+    template <typename U>
+    Defer(U &&f) : mThunk(std::forward<U>(f)) {}
+    ~Defer() { mThunk(); }
+
+private:
+    const std::function<void()> mThunk;
+};
+
 /**
  * Media Metrics BaseItem
  *

services/mediametrics/tests/mediametrics_tests.cpp

@@ -35,6 +35,23 @@ static size_t countNewlines(const char *s) {
     return count;
 }
 
+TEST(mediametrics_tests, startsWith) {
+  std::string s("test");
+  ASSERT_EQ(true, android::mediametrics::startsWith(s, "te"));
+  ASSERT_EQ(true, android::mediametrics::startsWith(s, std::string("tes")));
+  ASSERT_EQ(false, android::mediametrics::startsWith(s, "ts"));
+  ASSERT_EQ(false, android::mediametrics::startsWith(s, std::string("est")));
+}
+
+TEST(mediametrics_tests, defer) {
+  bool check = false;
+  {
+      android::mediametrics::Defer defer([&] { check = true; });
+      ASSERT_EQ(false, check);
+  }
+  ASSERT_EQ(true, check);
+}
+
 TEST(mediametrics_tests, instantiate) {
   sp mediaMetrics = new MediaMetricsService();
   status_t status;