Introduce ArrayView::subview function

webrtc/base/array_view.h

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 102 matching lines @@
   T& operator[](size_t idx) const {
     RTC_DCHECK_LT(idx, size_);
     RTC_DCHECK(data_);  // Follows from size_ > idx and the class invariant.
     return data_[idx];
   }
   T* begin() const { return data_; }
   T* end() const { return data_ + size_; }
   const T* cbegin() const { return data_; }
   const T* cend() const { return data_ + size_; }
 
+  ArrayView subview(size_t offset, size_t size) const {
+    if (offset >= size_)
+      return ArrayView();
+    return ArrayView(data_ + offset, std::min(size, size_ - offset));
+  }
+  ArrayView subview(size_t offset) const { return subview(offset, size_); }
+
   // Comparing two ArrayViews compares their (pointer,size) pairs; it does
   // *not* dereference the pointers.
   friend bool operator==(const ArrayView& a, const ArrayView& b) {
     return a.data_ == b.data_ && a.size_ == b.size_;
   }
   friend bool operator!=(const ArrayView& a, const ArrayView& b) {
     return !(a == b);
   }
 
  private:
   // Invariant: !data_ iff size_ == 0.
   void CheckInvariant() const { RTC_DCHECK_EQ(!data_, size_ == 0); }
   T* data_;
   size_t size_;
 };
 
 template <typename T>
 inline ArrayView<T> MakeArrayView(T* data, size_t size) {
   return ArrayView<T>(data, size);
 }
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_ARRAY_VIEW_H_