Fill in pprof time_nanos from profile timestamp

So when you open a profile with pprof, it gives you the time the profile
was taken:

```
$ pprof pprof.profile
...
Time: Jan 18, 2018 at 8:45pm (AEDT)
```

BUG: 202799418
Change-Id: I9953b7f42cc587af4efc95ae3ec7161b9f2173d8

2 files changed, 6 insertions, 0 deletions

diff --git a/simpleperf/scripts/pprof_proto_generator.py b/simpleperf/scripts/pprof_proto_generator.py
index b2ca0901..a9418105 100755
--- a/simpleperf/scripts/pprof_proto_generator.py
+++ b/simpleperf/scripts/pprof_proto_generator.py
@@ -315,6 +315,8 @@ class PprofProfileGenerator(object):
           comments.append("App Version Code:\n" + meta_info["app_versioncode"])
         for comment in comments:
             self.profile.comment.append(self.get_string_id(comment))
+        if "timestamp" in meta_info:
+            self.profile.time_nanos = int(meta_info["timestamp"]) * 1000 * 1000 * 1000
 
         numbers_re = re.compile(r"\d+")
 
diff --git a/simpleperf/scripts/test/pprof_proto_generator_test.py b/simpleperf/scripts/test/pprof_proto_generator_test.py
index 297cf149..d72f75f5 100644
--- a/simpleperf/scripts/test/pprof_proto_generator_test.py
+++ b/simpleperf/scripts/test/pprof_proto_generator_test.py
@@ -96,6 +96,10 @@ class TestPprofProtoGenerator(TestBase):
         """ Test the build ids generated are not padded with zeros. """
         self.assertIn('build_id: e3e938cc9e40de2cfe1a5ac7595897de(', self.run_generator())
 
+    def test_time_nanos(self):
+        """ Test the timestamp is adjusted to be nanoseconds. """
+        self.assertIn('time_nanos: 1516268753000000000\n', self.run_generator())
+
     def test_build_id_with_binary_cache(self):
         """ Test the build ids for elf files in binary_cache are not padded with zero. """
         # Test with binary_cache.