Add memory stats for linux page cycler. On linux, we collect

base/process_util.h

Index: base/process_util.h
diff --git a/base/process_util.h b/base/process_util.h
index fe1b4d2b42001ddd6f49226b9c0f0f857ab13623..7801d4c57959a6da4d2260102d9193e23f72cdb6 100644
--- a/base/process_util.h
+++ b/base/process_util.h
@@ -323,12 +323,16 @@ class ProcessMetrics {
   ~ProcessMetrics();
 
   // Returns the current space allocated for the pagefile, in bytes (these pages
-  // may or may not be in memory).
+  // may or may not be in memory).  On Linux, this returns the total virtual
+  // memory size.
   size_t GetPagefileUsage() const;
   // Returns the peak space allocated for the pagefile, in bytes.
   size_t GetPeakPagefileUsage() const;
-  // Returns the current working set size, in bytes.
+  // Returns the current working set size, in bytes.  On Linux, this returns
+  // the resident set size.
   size_t GetWorkingSetSize() const;
+  // Returns the peak working set size, in bytes.
+  size_t GetPeakWorkingSetSize() const;
   // Returns private usage, in bytes. Private bytes is the amount
   // of memory currently allocated to a process that cannot be shared.
   // Note: returns 0 on unsupported OSes: prior to XP SP2.