clang/win: Fix -Wextra warnings in webrtc.

webrtc/modules/desktop_capture/win/screen_capturer_win_magnifier.cc

Index: webrtc/modules/desktop_capture/win/screen_capturer_win_magnifier.cc
diff --git a/webrtc/modules/desktop_capture/win/screen_capturer_win_magnifier.cc b/webrtc/modules/desktop_capture/win/screen_capturer_win_magnifier.cc
index db40478023f8e7a7833ad1b5be47454442b12bfa..6639febc33061ab1cf742a71b416046837cc4b31 100644
--- a/webrtc/modules/desktop_capture/win/screen_capturer_win_magnifier.cc
+++ b/webrtc/modules/desktop_capture/win/screen_capturer_win_magnifier.cc
@@ -33,7 +33,8 @@ static LPCTSTR kHostWindowName = L"MagnifierHost";
 static LPCTSTR kMagnifierWindowClass = L"Magnifier";
 static LPCTSTR kMagnifierWindowName = L"MagnifierWindow";
 
-Atomic32 ScreenCapturerWinMagnifier::tls_index_(TLS_OUT_OF_INDEXES);
+int32_t kTlsIndexNotSet = 0;  // Should not be a valid pointer.

[Sergey Ulanov, 2015/12/09 22:31:51]

Not sure we can use 0 here. Can TlsAlloc() return 0?

[Nico, 2015/12/10 15:05:46]

Hm, you're right. Reverted this to patch set 1.

[Sergey Ulanov, 2015/12/10 17:29:55]

Sorry for not being clear, what I was suggesting initially is to define
kTlsIndexNotSet = static_cast<int32_t>(TLS_OUT_OF_INDEXES), which is the same as
-1.

+Atomic32 ScreenCapturerWinMagnifier::tls_index_(kTlsIndexNotSet);
 
 ScreenCapturerWinMagnifier::ScreenCapturerWinMagnifier(
     rtc::scoped_ptr<ScreenCapturer> fallback_capturer)
@@ -236,7 +237,7 @@ BOOL ScreenCapturerWinMagnifier::OnMagImageScalingCallback(
     RECT unclipped,
     RECT clipped,
     HRGN dirty) {
-  assert(tls_index_.Value() != TLS_OUT_OF_INDEXES);
+  assert(tls_index_.Value() != kTlsIndexNotSet);
 
   ScreenCapturerWinMagnifier* owner =
       reinterpret_cast<ScreenCapturerWinMagnifier*>(
@@ -369,15 +370,15 @@ bool ScreenCapturerWinMagnifier::InitializeMagnifier() {
     }
   }
 
-  if (tls_index_.Value() == TLS_OUT_OF_INDEXES) {
+  if (tls_index_.Value() == kTlsIndexNotSet) {
     // More than one threads may get here at the same time, but only one will
     // write to tls_index_ using CompareExchange.
     DWORD new_tls_index = TlsAlloc();
-    if (!tls_index_.CompareExchange(new_tls_index, TLS_OUT_OF_INDEXES))
+    if (!tls_index_.CompareExchange(new_tls_index, kTlsIndexNotSet))
       TlsFree(new_tls_index);
   }
 
-  assert(tls_index_.Value() != TLS_OUT_OF_INDEXES);
+  assert(tls_index_.Value() != kTlsIndexNotSet);
   TlsSetValue(tls_index_.Value(), this);
 
   magnifier_initialized_ = true;