Create rtc::AtomicInt POD struct.

Prevents accidental non-atomic reads, increments and stores since
"volatile int" doesn't enforce atomic usage.

BUG=
R=kwiberg@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1420043008

Cr-Commit-Position: refs/heads/master@{#10657}

webrtc/base/atomicops.h

@@ -20,7 +20,10 @@
 #include <windows.h>
 #endif  // defined(WEBRTC_WIN)
 
+#include "webrtc/base/constructormagic.h"
+
 namespace rtc {
+
 class AtomicOps {
  public:
 #if defined(WEBRTC_WIN)
@@ -61,8 +64,46 @@ class AtomicOps {
 #endif
 };
 
+// POD struct version of AtomicOps, prevents accidental non-atomic operator
+// usage (such as ++, -- or =). Functions are static, so that the AtomicInt::
+// prefix must be present in the code, clearly labeling the operations as
+// atomic.
+struct AtomicInt {
+  AtomicInt() : AtomicInt(0) {}
+  explicit AtomicInt(int value) : value_(value) {}
 
+  // Atomically increments |i|, returns the resulting incremented value.
+  static int Increment(AtomicInt* i) {
+    return AtomicOps::Increment(&i->value_);
+  }
 
+  // Atomically decrements |i|, returns the resulting decremented value.
+  static int Decrement(AtomicInt* i) {
+    return AtomicOps::Decrement(&i->value_);
+  }
+
+  // Atomically loads |i|.
+  static int AcquireLoad(const AtomicInt* i) {
+    return AtomicOps::AcquireLoad(&i->value_);
+  }
+
+  // Atomically stores |value| in |i|.
+  static void ReleaseStore(AtomicInt* i, int value) {
+    AtomicOps::ReleaseStore(&i->value_, value);
+  }
+
+  // Attempts to compare-and-swaps |old_value| for |new_value| in |i| , returns
+  // |i|'s initial value. If equal to |old_value|, then the CAS succeeded,
+  // otherwise no operation is performed.
+  static int CompareAndSwap(AtomicInt* i, int old_value, int new_value) {
+    return AtomicOps::CompareAndSwap(&i->value_, old_value, new_value);
+  }
+
+ private:
+  volatile int value_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(AtomicInt);
+};
 }
 
 #endif  // WEBRTC_BASE_ATOMICOPS_H_