Issue #2323 - Part 1: Add Min()/Max() methods to TimeDuration.

Just some helper functions to make time comparisons in the correct data
format easier.

See BZ 1321885

mozglue/misc/TimeStamp.h

@@ -7,6 +7,7 @@
 #define mozilla_TimeStamp_h
 
 #include <stdint.h>
+#include <algorithm>  // for std::min, std::max
 #include "mozilla/Assertions.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/FloatingPoint.h"
@@ -173,6 +174,17 @@ public:
 
     return FromTicks(ticks);
   }
+  static BaseTimeDuration Max(const BaseTimeDuration& aA,
+                              const BaseTimeDuration& aB)
+  {
+    return FromTicks(std::max(aA.mValue, aB.mValue));
+  }
+  static BaseTimeDuration Min(const BaseTimeDuration& aA,
+                              const BaseTimeDuration& aB)
+  {
+    return FromTicks(std::min(aA.mValue, aB.mValue));
+  }
+
 
 private:
   // Block double multiplier (slower, imprecise if long duration) - Bug 853398.