rtc::Buffer: Rename length to size, for conformance with the STL

And add a constructor for creating an uninitialized Buffer of a
specified size.

(I intend to follow up with more Buffer changes, but since it's rather
widely used, the rename is quite noisy and works better as a separate
CL.)

R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/48579004

Cr-Commit-Position: refs/heads/master@{#8841}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8841 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/buffer.cc

@@ -16,16 +16,20 @@ Buffer::Buffer() {
   Construct(NULL, 0, 0);
 }
 
-Buffer::Buffer(const void* data, size_t length) {
-  Construct(data, length, length);
+Buffer::Buffer(size_t size) : Buffer() {
+  SetSize(size);
 }
 
-Buffer::Buffer(const void* data, size_t length, size_t capacity) {
-  Construct(data, length, capacity);
+Buffer::Buffer(const void* data, size_t size) {
+  Construct(data, size, size);
+}
+
+Buffer::Buffer(const void* data, size_t size, size_t capacity) {
+  Construct(data, size, capacity);
 }
 
 Buffer::Buffer(const Buffer& buf) {
-  Construct(buf.data(), buf.length(), buf.length());
+  Construct(buf.data(), buf.size(), buf.size());
 }
 
 Buffer::~Buffer() = default;