Enable SysInfo::AmountOfPhysicalMemory to be called from within the Linux sandbox.

base/sys_info_linux.cc

Index: base/sys_info_linux.cc
diff --git a/base/sys_info_linux.cc b/base/sys_info_linux.cc
index acc477134cd38bed2ba37e6add9f84370bfc87ca..8237d1050d3f62a8fcc4e489fc2c2ae9762ea2d8 100644
--- a/base/sys_info_linux.cc
+++ b/base/sys_info_linux.cc
@@ -28,7 +28,13 @@ namespace base {
 
 // static
 int64 SysInfo::AmountOfPhysicalMemory() {
-  return AmountOfMemory(_SC_PHYS_PAGES);
+  static int64 physical_memory;
+  static bool physical_memory_valid = false;
+  if (!physical_memory_valid) {

[jar (doing other things), 2013/10/18 19:24:14]

I'm hopeful this is done on only one thread... as this would not be thread safe.

Can you verify that?  DCHECK it?

[jln (very slow on Chromium), 2013/10/18 21:08:42]

Should we just use LazyInstance these things? It's a bit expensive, but none of
these are hot.

[jar (doing other things), 2013/10/18 22:19:30]

+1.  If in doubt about multi-threading, I'd rather see lazy instance.  I don't
think the cost is actually that high, and probably not large considering it is
caching the answer, and replacing code that probably used to take longer to find
the answer again and again.

+    physical_memory = AmountOfMemory(_SC_PHYS_PAGES);
+    physical_memory_valid = true;
+  }
+  return physical_memory;
 }
 
 // static