Unified the structure of VirtualMemory implementations across platforms a bit.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index af47d05b88b8aff7d7eb8687e95a58bfd0200f82..20d1be996823b8033dbeb81733bc32a4b1d87d4e 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -643,12 +643,12 @@ int OS::StackWalk(Vector<OS::StackFrame> frames) {
 static const int kMmapFd = -1;
 static const int kMmapFdOffset = 0;
 
+
 VirtualMemory::VirtualMemory() : address_(NULL), size_(0) { }
 
-VirtualMemory::VirtualMemory(size_t size) {
-  address_ = ReserveRegion(size);
-  size_ = size;
-}
+
+VirtualMemory::VirtualMemory(size_t size)
+    : address_(ReserveRegion(size)), size_(size) { }
 
 
 VirtualMemory::VirtualMemory(size_t size, size_t alignment)