document yosemite API usage

Author: JeffryBooher

appshell/cefclient_mac.mm

@@ -222,9 +222,9 @@ -(void)windowTitleDidChange:(NSString*)title {
 }
 
 -(BOOL)isRunningOnYosemite {
-  NSDictionary * dict = [NSDictionary dictionaryWithContentsOfFile:@"/System/Library/CoreServices/SystemVersion.plist"];
-  NSString *version =  [dict objectForKey:@"ProductVersion"];
-  return ([version hasPrefix:@"10.10"]);
+    // this API returns nil prior to Yosemite
+    NSDictionary * dict = [NSDictionary dictionaryWithContentsOfFile:@"/System/Library/CoreServices/SystemVersion.plist"];
+    return dict != nil;
 }
 
 - (BOOL)isFullScreenSupported {

appshell/client_handler_mac.mm

@@ -165,14 +165,12 @@ - (void)setIsReallyClosing {
   isReallyClosing = true;
 }
 
-//
 -(BOOL)isRunningOnYosemite {
+    // this API returns nil prior to Yosemite
     NSDictionary * dict = [NSDictionary dictionaryWithContentsOfFile:@"/System/Library/CoreServices/SystemVersion.plist"];
-    NSString *version =  [dict objectForKey:@"ProductVersion"];
-    return ([version hasPrefix:@"10.10"]);
+    return dict != nil;
 }
 
-
 - (BOOL)isFullScreenSupported {
     // Return False on Yosemite so we
     //  don't draw our own full screen button