Create a field trial to test if we can detect good QPC implementations.

base/cpu.cc

Index: base/cpu.cc
diff --git a/base/cpu.cc b/base/cpu.cc
index d6976bab33b316aed50e3a133edf1a7e8a060a97..4a94af09bd1ee8aff00a1bb51feb91c727909c8a 100644
--- a/base/cpu.cc
+++ b/base/cpu.cc
@@ -32,6 +32,7 @@ CPU::CPU()
     has_ssse3_(false),
     has_sse41_(false),
     has_sse42_(false),
+    has_non_stop_time_stamp_counter_(false),
     cpu_vendor_("unknown") {
   Initialize();
 }
@@ -123,6 +124,7 @@ void CPU::Initialize() {
   // Get the brand string of the cpu.
   __cpuid(cpu_info, 0x80000000);
   const int parameter_end = 0x80000004;
+  int max_parameter = cpu_info[0];
 
   if (cpu_info[0] >= parameter_end) {
     char* cpu_string_ptr = cpu_string;
@@ -135,6 +137,12 @@ void CPU::Initialize() {
     }
     cpu_brand_.assign(cpu_string, cpu_string_ptr - cpu_string);
   }
+
+  const int parameter_containing_non_stop_time_stamp_counter = 0x80000007;
+  if (max_parameter >= parameter_containing_non_stop_time_stamp_counter) {
+    __cpuid(cpu_info, parameter_containing_non_stop_time_stamp_counter);
+    has_non_stop_time_stamp_counter_ = (cpu_info[3] & (1 << 8)) != 0;
+  }
 #endif
 }