[heap] Non-contiguous young generation

src/base/platform/platform.h

Index: src/base/platform/platform.h
diff --git a/src/base/platform/platform.h b/src/base/platform/platform.h
index 4993dc861474339d5c0202d6f76138abf32ae632..5b2dbc9a0b29831865f082ce0fd25024754ff541 100644
--- a/src/base/platform/platform.h
+++ b/src/base/platform/platform.h
@@ -291,6 +291,10 @@ class VirtualMemory {
   // by address().
   VirtualMemory(size_t size, size_t alignment);
 
+  // Construct a virtual memory by assigning it some already mapped address
+  // and size.
+  VirtualMemory(void* address, size_t size) : address_(address), size_(size) {}
+
   // Releases the reserved memory, if any, controlled by this VirtualMemory
   // object.
   ~VirtualMemory();