Replace manual casting to rvalue reference with calls to std::move

Review URL: https://codereview.webrtc.org/1570473002

Cr-Commit-Position: refs/heads/master@{#11163}

webrtc/system_wrappers/include/scoped_vector.h

@@ -43,9 +43,7 @@ class ScopedVector {
   ~ScopedVector() { clear(); }
 
   // Move construction and assignment.
-  ScopedVector(ScopedVector&& other) {
-    *this = static_cast<ScopedVector&&>(other);
-  }
+  ScopedVector(ScopedVector&& other) { *this = std::move(other); }
   ScopedVector& operator=(ScopedVector&& other) {
     std::swap(v_, other.v_);  // The arguments are std::vectors, so std::swap
                               // is the one that we want.
@@ -58,7 +56,7 @@ class ScopedVector {
   ScopedVector& operator=(const ScopedVector& other) = delete;
 
   // Get an rvalue reference. (sv.Pass() does the same thing as std::move(sv).)
-  ScopedVector&& Pass() { return static_cast<ScopedVector&&>(*this); }
+  ScopedVector&& Pass() { return std::move(*this); }
 
   reference operator[](size_t index) { return v_[index]; }
   const_reference operator[](size_t index) const { return v_[index]; }