Fix the WebString leak in MockWebClipboardImpl

When we run content_shell in the single process mode with tests using the clipboard, the renderer thread passes WebString to the browser thread. It causes leak.
To avoid this, change the member WebString to NullableString16.

BUG=328158
TEST=content_shell --dump-render-tree --single-process ../../third_party/WebKit/LayoutTests/editing/pasteboard/createMarkup-assert.xml

Review URL: https://codereview.chromium.org/135853010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247850 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247850
Update HPACK implementation to draft 05

In particular:

 - Switch to 1-based indexing.
 - Use 0 instead of -1 as the "invalid index" value.
 - Add "host" header to the static table.
 - Add HpackEncodingContext::GetMutableEntryCount() function.

This lands server change 60493594 by akalin.

Review URL: https://codereview.chromium.org/145353017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247851 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247851