Support saving browser metrics to disk and reading them during next run.

base/metrics/persistent_memory_allocator.h

Index: base/metrics/persistent_memory_allocator.h
diff --git a/base/metrics/persistent_memory_allocator.h b/base/metrics/persistent_memory_allocator.h
index 4c0db5264a8f810721653d130c6428437ef5f9aa..56edd2ca24e0131d633b7aea805bd80e3681cb66 100644
--- a/base/metrics/persistent_memory_allocator.h
+++ b/base/metrics/persistent_memory_allocator.h
@@ -12,6 +12,7 @@
 
 #include "base/atomicops.h"
 #include "base/base_export.h"
+#include "base/files/file_path.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
@@ -126,6 +127,10 @@ class BASE_EXPORT PersistentMemoryAllocator {
     kTypeIdAny = 0  // Match any type-id inside GetAsObject().
   };
 
+  // This is the standard file extension (suitable for being passed to the
+  // AddExtension() method of base::FilePath) for dumps of persistent memory.
+  static const base::FilePath::CharType kFileExtension[];
+
   // The allocator operates on any arbitrary block of memory. Creation and
   // persisting or sharing of that block with another process is the
   // responsibility of the caller. The allocator needs to know only the
@@ -191,6 +196,7 @@ class BASE_EXPORT PersistentMemoryAllocator {
   // not guarantee consistency. Use with care. Do not write.
   const void* data() const { return const_cast<const char*>(mem_base_); }
   size_t length() const { return mem_size_; }
+  size_t size() const { return mem_size_; }
   size_t used() const;
 
   // Get an object referenced by a |ref|. For safety reasons, the |type_id|