crypto: disable NSS AES-NI support when AVX is disabled by OS.

base/cpu.h

Index: base/cpu.h
diff --git a/base/cpu.h b/base/cpu.h
index 509763e170f4c666089f65db1b5b81097de452a9..23aa1c46171c235eec1411aaa606c085f8783820 100644
--- a/base/cpu.h
+++ b/base/cpu.h
@@ -46,6 +46,10 @@ class BASE_EXPORT CPU {
   bool has_sse41() const { return has_sse41_; }
   bool has_sse42() const { return has_sse42_; }
   bool has_avx() const { return has_avx_; }
+  // has_avx_hardware returns true when AVX is present in the CPU. This might
+  // differ from the value of |has_avx()| because |has_avx()| also tests for
+  // operating system support needed to actually call AVX instuctions.
+  bool has_avx_hardware() const { return has_avx_hardware_; }

[wtc, 2013/11/21 21:03:44]

I don't think has_avx_hardware() will be useful, except for some sort of CPU
info UI. Does such UI exist in Chrome? For Chrome, has_avx() should be
sufficient. So I recommend not adding has_avx_hardware().

Update: I see that we need has_avx_hardware() for our workaround for the NSS
bug. Perhaps we should add a comment to discourage people from using
has_avx_hardware() in a general setting.

[agl, 2013/11/22 16:22:35]

Done.

   bool has_non_stop_time_stamp_counter() const {
     return has_non_stop_time_stamp_counter_;
   }
@@ -71,6 +75,7 @@ class BASE_EXPORT CPU {
   bool has_sse41_;
   bool has_sse42_;
   bool has_avx_;
+  bool has_avx_hardware_;
   bool has_non_stop_time_stamp_counter_;
   std::string cpu_vendor_;
   std::string cpu_brand_;