Made rtc::Optional a bit more like std::optional.

webrtc/base/optional.h

Index: webrtc/base/optional.h
diff --git a/webrtc/base/optional.h b/webrtc/base/optional.h
index 25cfbfe41752597d340864f3cc46ce56794763b4..add6fa9181b192f15aa33163972a42c1be26e31b 100644
--- a/webrtc/base/optional.h
+++ b/webrtc/base/optional.h
@@ -62,10 +62,10 @@ class Optional final {
   Optional() : has_value_(false) {}
 
   // Construct an Optional that contains a value.
-  explicit Optional(const T& value) : has_value_(true) {
+  Optional(const T& value) : has_value_(true) {

[tommi, 2016/06/16 16:08:22]

this goes against the style guide though.  Is requiring explicit causing
problems?

[kwiberg-webrtc, 2016/06/16 17:26:42]

It's very convenient to have T convert implicitly to Optional<T>, and it's what
std::optional does. The standard library violates our style guide quite a lot...

     new (&value_) T(value);
   }
-  explicit Optional(T&& value) : has_value_(true) {
+  Optional(T&& value) : has_value_(true) {
     new (&value_) T(std::move(value));
   }
 
@@ -186,6 +186,22 @@ class Optional final {
                                           : m1.has_value_ != m2.has_value_;
   }
 
+  friend bool operator==(const Optional& opt, const T& val) {
+    return opt.has_value_ && opt.value_ == val;
+  }
+
+  friend bool operator==(const T& val, const Optional& opt) {
+    return opt == val;
+  }
+
+  friend bool operator!=(const Optional& opt, const T& val) {
+    return !(opt == val);
+  }
+
+  friend bool operator!=(const T& val, const Optional& opt) {
+    return !(opt == val);
+  }
+
  private:
   bool has_value_;  // True iff value_ contains a live value.
   union {