Use a static variable to store creation time of first run.

Calling GetFileInfo() is a blocking call and because the desktop feature
tracker needs the first run creation time, it was performing file I/O on
the UI thread causing jank. This change moves getting the creation time to
sentinel creation and caches that result in a static variable.

Bug: 785189
Change-Id: Ia4b4e5783bf3e6d06c9812661d7930384cbf9b21
Reviewed-on: https://chromium-review.googlesource.com/773445Reviewed-by: Carlos Pizano <cpu@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Bettina Dea <bdea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517914}

chrome/browser/first_run/first_run.cc

@@ -423,6 +423,19 @@ void ProcessDefaultBrowserPolicy(bool make_chrome_default_for_user) {
   }
 }
 
+// Reads the creation time of the first run sentinel file. If the first run
+// sentinel file does not exist, it will return base::Time().
+base::Time ReadFirstRunSentinelCreationTime() {
+  base::Time first_run_sentinel_creation_time = base::Time();
+  base::FilePath first_run_sentinel;
+  if (first_run::internal::GetFirstRunSentinelFilePath(&first_run_sentinel)) {
+    base::File::Info info;
+    if (base::GetFileInfo(first_run_sentinel, &info))
+      first_run_sentinel_creation_time = info.creation_time;
+  }
+  return first_run_sentinel_creation_time;
+}
+
 }  // namespace
 
 namespace first_run {
@@ -555,17 +568,15 @@ bool IsMetricsReportingOptIn() {
 void CreateSentinelIfNeeded() {
   if (IsChromeFirstRun())
     internal::CreateSentinel();
+
+  // Causes the first run sentinel creation time to be read and cached, while
+  // I/O is still allowed.
+  ignore_result(GetFirstRunSentinelCreationTime());
 }
 
 base::Time GetFirstRunSentinelCreationTime() {
-  base::FilePath first_run_sentinel;
-  base::Time first_run_sentinel_creation_time = base::Time();
-  if (first_run::internal::GetFirstRunSentinelFilePath(&first_run_sentinel)) {
-    base::File::Info info;
-    if (base::GetFileInfo(first_run_sentinel, &info))
-      first_run_sentinel_creation_time = info.creation_time;
-  }
-  return first_run_sentinel_creation_time;
+  static const base::Time cached_time = ReadFirstRunSentinelCreationTime();
+  return cached_time;
 }
 
 bool SetShowFirstRunBubblePref(FirstRunBubbleOptions show_bubble_option) {

chrome/browser/first_run/first_run.h

@@ -115,8 +115,8 @@ bool IsMetricsReportingOptIn();
 // (http://crbug.com/264694).
 void CreateSentinelIfNeeded();
 
-// Returns the creation time of the first run sentinel file. If the first run
-// sentinel file does not exist, it will return base::Time().
+// Returns the first run sentinel creation time. This only requires I/O
+// permission on the sequence it is first called on.
 base::Time GetFirstRunSentinelCreationTime();
 
 // Sets the kShowFirstRunBubbleOption local state pref so that the browser