Bug 1333686 - Part 3: Fix -Wmacro-redefined warnings in ipc/chromium. r=jld

The WARN_UNUSED_RESULT macro is defined in multiple Google header files in ipc/chromium and webrtc. Copy the WARN_UNUSED_RESULT definition from the latest security/sandbox/chromium/base/compiler_specific.h to our ipc/chromium code. Also remove the ALLOW_UNUSED macro definition because it is no longer defined in the latest compiler_specific.h and is not used anywhere.

Warning: -Wmacro-redefined in ipc/chromium/src/base/compiler_specific.h: 'WARN_UNUSED_RESULT' macro redefined
ipc/chromium/src/base/compiler_specific.h:73:9: warning: 'WARN_UNUSED_RESULT' macro redefined [-Wmacro-redefined]
#define WARN_UNUSED_RESULT __attribute__((warn_unused_result))

media/webrtc/trunk/webrtc/typedefs.h:152:9: note: previous definition is here
#define WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))

MozReview-Commit-ID: EUIlXGKLhDL

--HG--
extra : rebase_source : 4c584dfa2243514aef0357ff919d1cba48bd8b86

ipc/chromium/src/base/compiler_specific.h

@@ -67,12 +67,14 @@
 
 #endif  // COMPILER_MSVC
 
-
-#if defined(COMPILER_GCC)
-#define ALLOW_UNUSED __attribute__((unused))
+// Annotate a function indicating the caller must examine the return value.
+// Use like:
+//   int foo() WARN_UNUSED_RESULT;
+// To explicitly ignore a result, see |ignore_result()| in base/macros.h.
+#undef WARN_UNUSED_RESULT
+#if defined(COMPILER_GCC) || defined(__clang__)
 #define WARN_UNUSED_RESULT __attribute__((warn_unused_result))
-#else  // Not GCC
-#define ALLOW_UNUSED
+#else
 #define WARN_UNUSED_RESULT
 #endif