Simple Cache: restore the high-res timer

This *reverts* the parts of high-res timing that was moved out from simple cache
in attempt to have it in base/, here:
http://src.chromium.org/viewvc/chrome?view=revision&revision=216478

The changes in base/ are untouched today. This partial revert should be safe
because this change just adds (un-removes) a different implementation and
switches simple cache to using it.

The bug being blocked by this deficiency is in the BUG field, we do not have a
specific bug for the problem, it would have required age restriction on the
audience.

BUG=261618

Review URL: https://chromiumcodereview.appspot.com/23819025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221492 0039d316-1c4b-4281-b951-d872f2087c98

net/disk_cache/simple/simple_util.cc

@@ -21,6 +21,25 @@ namespace {
 // Size of the uint64 hash_key number in Hex format in a string.
 const size_t kEntryHashKeyAsHexStringSize = 2 * sizeof(uint64);
 
+// TODO(clamy, gavinp): this should go in base
+bool GetNanoSecsFromStat(const struct stat& st,
+                         time_t* out_sec,
+                         long* out_nsec) {
+#if defined(OS_ANDROID)
+  *out_sec = st.st_mtime;
+  *out_nsec = st.st_mtime_nsec;
+#elif defined(OS_LINUX)
+  *out_sec = st.st_mtim.tv_sec;
+  *out_nsec = st.st_mtim.tv_nsec;
+#elif defined(OS_MACOSX) || defined(OS_IOS) || defined(OS_BSD)
+  *out_sec = st.st_mtimespec.tv_sec;
+  *out_nsec = st.st_mtimespec.tv_nsec;
+#else
+  return false;
+#endif
+  return true;
+}
+
 }  // namespace
 
 namespace disk_cache {
@@ -88,6 +107,20 @@ int64 GetFileOffsetFromKeyAndDataOffset(const std::string& key,
 // TODO(clamy, gavinp): this should go in base
 bool GetMTime(const base::FilePath& path, base::Time* out_mtime) {
   DCHECK(out_mtime);
+#if defined(OS_POSIX)
+  base::ThreadRestrictions::AssertIOAllowed();
+  struct stat file_stat;
+  if (stat(path.value().c_str(), &file_stat) != 0)
+    return false;
+  time_t sec;
+  long nsec;
+  if (GetNanoSecsFromStat(file_stat, &sec, &nsec)) {
+    int64 usec = (nsec / base::Time::kNanosecondsPerMicrosecond);
+    *out_mtime = base::Time::FromTimeT(sec)
+        + base::TimeDelta::FromMicroseconds(usec);
+    return true;
+  }
+#endif
   base::PlatformFileInfo file_info;
   if (!file_util::GetFileInfo(path, &file_info))
     return false;

net/disk_cache/simple/simple_util.h

@@ -63,8 +63,8 @@ NET_EXPORT_PRIVATE int64 GetFileOffsetFromKeyAndDataOffset(
     const std::string& key,
     int data_offset);
 
-// Fills |out_time| with the time the file last modified time.
-// TODO(gavinp): Remove this function.
+// Fills |out_time| with the time the file last modified time. Unlike the
+// functions in platform_file.h, the time resolution is milliseconds.
 NET_EXPORT_PRIVATE bool GetMTime(const base::FilePath& path,
                                  base::Time* out_mtime);
 }  // namespace simple_backend