Bug 816117 - Part 3: Only get control registers from the profiled thread. r=bgirard

tools/profiler/platform-win32.cc

@@ -125,7 +125,7 @@ class SamplerThread : public Thread {
     if (SuspendThread(profiled_thread) == kSuspendFailed)
       return;
 
-    context.ContextFlags = CONTEXT_FULL;
+    context.ContextFlags = CONTEXT_CONTROL;
     if (GetThreadContext(profiled_thread, &context) != 0) {
 #if V8_HOST_ARCH_X64
       sample->pc = reinterpret_cast<Address>(context.Rip);