Ensure only whitelisted stubs have sse2 versions in the snapshot.

src/arm/assembler-arm.h

Index: src/arm/assembler-arm.h
diff --git a/src/arm/assembler-arm.h b/src/arm/assembler-arm.h
index 47dda2aa7224cd6622e997a1621fac6996a4cf2b..8caa64df34c2ce442b4919122c45b531dd06c864 100644
--- a/src/arm/assembler-arm.h
+++ b/src/arm/assembler-arm.h
@@ -64,23 +64,41 @@ class CpuFeatures : public AllStatic {
   // Check whether a feature is supported by the target CPU.
   static bool IsSupported(CpuFeature f) {
     ASSERT(initialized_);
-    return (supported_ & (1u << f)) != 0;
+    return Check(f, supported_);
   }
 
   static bool IsFoundByRuntimeProbingOnly(CpuFeature f) {
     ASSERT(initialized_);
-    return (found_by_runtime_probing_only_ &
-            (static_cast<uint64_t>(1) << f)) != 0;
+    return Check(f, found_by_runtime_probing_only_);
   }
 
   static bool IsSafeForSnapshot(CpuFeature f) {
-    return (IsSupported(f) &&
+    return Check(f, cross_compile_) ||
+           (IsSupported(f) &&
             (!Serializer::enabled() || !IsFoundByRuntimeProbingOnly(f)));
   }
 
   static unsigned cache_line_size() { return cache_line_size_; }
 
+  static bool VerifyCrossCompiling() {
+    return cross_compile_ == 0;
+  }
+
+  static bool VerifyCrossCompiling(CpuFeature f) {
+    unsigned mask = flag2set(f);
+    return cross_compile_ == 0 ||
+           (cross_compile_ & mask) == mask;
+  }
+
  private:
+  static bool Check(CpuFeature f, unsigned set) {
+    return (set & flag2set(f)) != 0;
+  }
+
+  static unsigned flag2set(CpuFeature f) {
+    return 1u << f;
+  }
+
 #ifdef DEBUG
   static bool initialized_;
 #endif
@@ -88,6 +106,8 @@ class CpuFeatures : public AllStatic {
   static unsigned found_by_runtime_probing_only_;
   static unsigned cache_line_size_;
 
+  static unsigned cross_compile_;
+
   friend class ExternalReference;
   friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);