WebVector requires some ceremony when used with types that do not have a default constructor, or types whose copying is expensive. I've been using the dance below.

std::vector<WebType> vector;
vector.reserve(final_size);
for (size_t i = 0; i < final_size; ++i)
  vector.emplace_back(...);
WebVector<WebType> web_vector(std::move(vector));

We should add emplace_back and any necessary supporting functions to WebVector, so we can construct elements directly into the vector's buffer. I'll put together a CL for this.
 

In a couple of scenarios, I find myself building a WebVector by first constructing a std::vector with the desired data, and then using the WebVector constructor that std::moves a std::vector in.

For example, WebVector's sized constructor cannot be used with types that do not have a default constructor, or for types that don't support moving and have an expensive copy operator. In that case, I've been doing the following dance.

std::vector<WebType> vector;
vector.reserve(final_size);
for (size_t i = 0; i < final_size; ++i)
  vector.emplace_back(...);
WebVector<WebType> web_vector(std::move(vector));

We should add any necessary supporting functions to WebVector so we can construct the vectors we need directly, without going through an std::vector. I will be submitting CLs for the cases I encounter.

So far, this bug covers:
* in-place construction via emplace_back, for types where default construction + assignment is expensive
* types without a default constructor
* resize() for use with std::unique