Move memory histograms generation to MetricsMemoryDetails.

chrome/browser/memory_details_mac.cc

Index: chrome/browser/memory_details_mac.cc
diff --git a/chrome/browser/memory_details_mac.cc b/chrome/browser/memory_details_mac.cc
index 8783a020a8e5c6cdea77e013e8f1f5e1ef9a99e2..8fe09083f53e283c35cc086c675528d6e8b813e9 100644
--- a/chrome/browser/memory_details_mac.cc
+++ b/chrome/browser/memory_details_mac.cc
@@ -48,10 +48,7 @@ enum BrowserType {
   MAX_BROWSERS
 } BrowserProcess;
 
-
-MemoryDetails::MemoryDetails()
-    : user_metrics_mode_(UPDATE_USER_METRICS),
-      memory_growth_tracker_(NULL) {
+MemoryDetails::MemoryDetails() {
   const base::FilePath browser_process_path =
       base::GetProcessExecutablePath(base::GetCurrentProcessHandle());
   const std::string browser_process_name =