Implement committed physical memory stats for Linux.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 92d928b328822aaec30f9b2dc421aa2a42050d56..72558d09ac4a364cfea1d32b5934f1aa760eb975 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -2766,6 +2766,7 @@ class V8EXPORT HeapStatistics {
   HeapStatistics();
   size_t total_heap_size() { return total_heap_size_; }
   size_t total_heap_size_executable() { return total_heap_size_executable_; }
+  size_t total_physical_size() { return total_physical_size_; }
   size_t used_heap_size() { return used_heap_size_; }
   size_t heap_size_limit() { return heap_size_limit_; }
 
@@ -2774,11 +2775,15 @@ class V8EXPORT HeapStatistics {
   void set_total_heap_size_executable(size_t size) {
     total_heap_size_executable_ = size;
   }
+  void set_total_physical_size(size_t size) {
+    total_physical_size_ = size;
+  }
   void set_used_heap_size(size_t size) { used_heap_size_ = size; }
   void set_heap_size_limit(size_t size) { heap_size_limit_ = size; }
 
   size_t total_heap_size_;
   size_t total_heap_size_executable_;
+  size_t total_physical_size_;
   size_t used_heap_size_;
   size_t heap_size_limit_;