Fix some clang warnings with -Wmissing-braces in base.

base/profiler/stack_sampling_profiler_win.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <objbase.h>
 #include <windows.h>
 
 #include <map>
 #include <utility>
 
@@ skipping 22 matching lines @@
   int i = 0;
   for (; (i < max_stack_size) && context->Rip; ++i) {
     // Try to look up unwind metadata for the current function.
     ULONG64 image_base;
     PRUNTIME_FUNCTION runtime_function =
         RtlLookupFunctionEntry(context->Rip, &image_base, nullptr);
 
     instruction_pointers[i] = reinterpret_cast<const void*>(context->Rip);
 
     if (runtime_function) {
-      KNONVOLATILE_CONTEXT_POINTERS nvcontext = {0};
+      KNONVOLATILE_CONTEXT_POINTERS nvcontext = {};
       void* handler_data;
       ULONG64 establisher_frame;
       RtlVirtualUnwind(0, image_base, context->Rip, runtime_function, context,
                        &handler_data, &establisher_frame, &nvcontext);
     } else {
       // If we don't have a RUNTIME_FUNCTION, then in theory this should be a
       // leaf function whose frame contains only a return address, at
       // RSP. However, crash data also indicates that some third party libraries
       // do not provide RUNTIME_FUNCTION information for non-leaf functions. We
       // could manually unwind the stack in the former case, but attempting to
@@ skipping 294 matching lines @@
 
   if (thread_handle) {
     return scoped_ptr<NativeStackSampler>(new NativeStackSamplerWin(
         win::ScopedHandle(thread_handle)));
   }
 #endif
   return scoped_ptr<NativeStackSampler>();
 }
 
 }  // namespace base