diff --git a/mozilla/xpcom/base/nsIMemory.idl b/mozilla/xpcom/base/nsIMemory.idl
index 83da99183e0..e5c04d361df 100644
--- a/mozilla/xpcom/base/nsIMemory.idl
+++ b/mozilla/xpcom/base/nsIMemory.idl
@@ -98,6 +98,13 @@ interface nsIMemory : nsISupports
      * @param obs - the observer to unregister
      */
     void unregisterObserver(in nsIMemoryPressureObserver obs);
+
+    /**
+     * This predicate can be used to determine if we're in a low-memory
+     * situation (what constitutes low-memory is platform dependent). This
+     * can be used to trigger the memory flushers.
+     */
+    boolean isLowMemory();
 };
 
 /**
diff --git a/mozilla/xpcom/base/nsMemoryImpl.cpp b/mozilla/xpcom/base/nsMemoryImpl.cpp
index eb3fefa1227..b6c116cbe6e 100644
--- a/mozilla/xpcom/base/nsMemoryImpl.cpp
+++ b/mozilla/xpcom/base/nsMemoryImpl.cpp
@@ -24,6 +24,10 @@
 #include "prmem.h"
 #include "nsIServiceManager.h"
 
+#ifdef XP_PC
+#include <windows.h>
+#endif
+
 NS_IMPL_THREADSAFE_ISUPPORTS1(nsMemoryImpl, nsIMemory)
 
 NS_METHOD
@@ -46,7 +50,7 @@ nsMemoryImpl::Create(nsISupports* outer, const nsIID& aIID, void* *aInstancePtr)
 ////////////////////////////////////////////////////////////////////////////////
 // Define NS_OUT_OF_MEMORY_TESTER if you want to force memory failures
 
-#ifdef DEBUG_warren
+#ifdef DEBUG_xwarren
 #define NS_OUT_OF_MEMORY_TESTER
 #endif
 
@@ -164,6 +168,20 @@ nsMemoryImpl::UnregisterObserver(nsIMemoryPressureObserver* obs)
     return mObservers->RemoveElement(obs);
 }
 
+NS_IMETHODIMP
+nsMemoryImpl::IsLowMemory(PRBool *result)
+{
+#ifdef XP_PC
+    MEMORYSTATUS stat;
+    GlobalMemoryStatus(&stat);
+    *result = ((float)stat.dwAvailPageFile / stat.dwTotalPageFile) < 0.1;
+    return NS_OK;
+#else
+    NS_NOTREACHED("nsMemoryImpl::IsLowMemory");
+    return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
 nsresult
 nsMemoryImpl::FlushMemory(PRUint32 reason, PRSize size)
 {