Modifies SDK and iOS detection for helper method that needs iOS 9+

webrtc/modules/utility/source/helpers_ios.mm

Index: webrtc/modules/utility/source/helpers_ios.mm
diff --git a/webrtc/modules/utility/source/helpers_ios.mm b/webrtc/modules/utility/source/helpers_ios.mm
index a312f032d13f6bd8460f04b8df904ef1a42dc316..b16c51e1e6cafd7648c22135243cf25884a26beb 100644
--- a/webrtc/modules/utility/source/helpers_ios.mm
+++ b/webrtc/modules/utility/source/helpers_ios.mm
@@ -23,6 +23,27 @@
 namespace webrtc {
 namespace ios {
 
+#define SYSTEM_VERSION_EQUAL_TO(v)           \
+  ([[[UIDevice currentDevice] systemVersion] \

[tkchin_webrtc, 2016/03/01 21:51:34]

can just use doubleValue to make these comparisons easier

[henrika_webrtc, 2016/03/02 14:49:50]

Great idea, thanks!

+       compare:v                             \
+       options:NSNumericSearch] == NSOrderedSame)
+#define SYSTEM_VERSION_GREATER_THAN(v)       \
+  ([[[UIDevice currentDevice] systemVersion] \
+       compare:v                             \
+       options:NSNumericSearch] == NSOrderedDescending)
+#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v) \
+  ([[[UIDevice currentDevice] systemVersion]       \
+       compare:v                                   \
+       options:NSNumericSearch] != NSOrderedAscending)
+#define SYSTEM_VERSION_LESS_THAN(v)          \
+  ([[[UIDevice currentDevice] systemVersion] \
+       compare:v                             \
+       options:NSNumericSearch] == NSOrderedAscending)
+#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v) \
+  ([[[UIDevice currentDevice] systemVersion]    \
+       compare:v                                \
+       options:NSNumericSearch] != NSOrderedDescending)
+
 // Internal helper method used by GetDeviceName() to return device name.
 const char* LookUpRealName(const char* raw_name) {
   // Lookup table which maps raw device names to real (human readable) names.
@@ -169,14 +190,23 @@ int GetProcessorCount() {
   return [NSProcessInfo processInfo].processorCount;
 }
 
+#if defined(__IPHONE_9_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_9_0
 bool GetLowPowerModeEnabled() {
-  NSProcessInfo* info = [NSProcessInfo processInfo];
   // lowPoweredModeEnabled is only available on iOS9+.
-  if ([info respondsToSelector:@selector(lowPoweredModeEnabled)]) {
-    return info.lowPowerModeEnabled;
-  }
-  return false;
+  if
+    SYSTEM_VERSION_LESS_THAN(@"9.0.0") {

[tkchin_webrtc, 2016/03/01 21:51:33]

Wouldn't use macros. Instead have a bunch of functions you can call with cached
value.

e.g.
double GetSystemVersion() {
  static dispatch_once once_token;
  static double system_version;
  dispatch_once(&once_token, ^{
    system_version = [UIDevice currentDevice].systemVersion.doubleValue;
  });
  return system_version;
}

then e.g.:

bool isIos9OrGreater() {
  return GetSystemVersion() >= 9.0;
}

[henrika_webrtc, 2016/03/02 14:49:50]

Done.

+      LOG(LS_WARNING) << "webrtc::ios::GetLowPowerModeEnabled() is not "
+                         "supported. Requires at least iOS 9.0";
+      return false;
+    }
+  NSProcessInfo* info = [NSProcessInfo processInfo];
+  return info.lowPowerModeEnabled;
 }
+#else
+// TODO(henrika): can't use iOS 9 APIs as the SDK version doesn't support

[tkchin_webrtc, 2016/03/01 21:51:34]

If it's unavailable we should just not use it. That means adding the
availability checks everywhere the function is used though.

[henrika_webrtc, 2016/03/02 14:49:50]

Done.

+// them. What is the best thing to do here? User will get linker error;
+// should be sufficient, right?
+#endif
 
 }  // namespace ios
 }  // namespace webrtc