Re-land: 178586 Avoid fragmenting address space on small windows systems.

Source/wtf/PageAllocator.cpp

Index: Source/wtf/PageAllocator.cpp
diff --git a/Source/wtf/PageAllocator.cpp b/Source/wtf/PageAllocator.cpp
index fda703aec591d619f15f31d7d7f3fb0740bac9a6..60a02f80ad6889e369acdc53129fce8affed472c 100644
--- a/Source/wtf/PageAllocator.cpp
+++ b/Source/wtf/PageAllocator.cpp
@@ -69,8 +69,11 @@ static bool shouldUseAddressHint()
     // is running under WOW64, then it has at least 3 GB available (and likely
     // 4 GB depending upon the OS version), and we want use the additional
     // randomness.
-    // TODO(tsepez): presently disabled due to IsWow64Process() compatibility.
-    return true;
+    static BOOL bIsWow64 = -1;
+    if (bIsWow64 == -1) {
+        IsWow64Process(GetCurrentProcess(), &bIsWow64);

[Chris Evans, 2014/11/18 18:29:31]

This function has a return value (success / fail). Maybe we want to explicitly
handle the "fail" case and hard wire an assumption that it's a 32-bit process in
that case?

We might also ASSERT() that it succeeds to get visibility in the debug trybot
runs that it's working ok?

+    }
+    return !!bIsWow64;
 #else // CPU(32BIT)
     return true;
 #endif // CPU(32BIT)