When synchronous mode specified (defualt), 
method blocked until file is produced. 
With asynchronous mode method returned and file will be produced in
background. 

One can call Canvas::SaveAs() several times, all specified files will be
created one by one asynchronously

It let configure more complex program arguments for starting browser for
the canvas, provide brief docu

By defauly, ROOT will try to crate local window with CEF or Qt5.
If not available, default browser will be started.
If place is specified, it should be program name like:
   canvas->Show("/usr/bin/opera");
   canvas->Show("firefox");

One could show canvas in several different places.

By default, TCanvas::Update() will block until latest canvas 
version delivered to all clients and displayed. Implement with
straight polling loop.

Each call to TCanvas::Modified() increments modify counter. 
This counter used in then next TCanvas::Update() call to identify
current version of canvas. TCanvas::IsModified() will return true 
until drawing is completed and painter confirms that last version of
canvas delivered to all clients and displayed. 

This commit also adds some minor improvements to method descriptions.
It introduces no functional changes.

The tests programs in these folders are not meant to be shown in the reference guide.
This fixes an issues with the TStopwatch doc which had multiple documentation  of the same method.

When chunking and fitting the right amount of elements per chunk you
may end up with empty chunks at the end. This chunks will still consist
of N elements per chunk, but they will not be initialized. Accessing
them was a problem. Solved by reducing the number of chunks (not
allowing empty chunks)

This removes the file dependency between LLVM and the git HEAD file,
which currently causes that we rebuild LLVM/Cling/Dictionaries
once someone does anything meaningful in git.

Currently LLVM LTO and other parts depend on the git HEAD file
because they pull in the current git revision (and should update
when the git revision changes). This is causing some unnecessary
rebuilding everytime someone is touching his git HEAD file.

This commit is disabling this in future LLVM versions by setting
the appropriate flag in LLVM to OFF (doesn't do a lot by now
as we first need to get this revision in the ROOT llvm version
https://reviews.llvm.org/D35377).

because two input parameters are not basic types.

The issue was mentioned here: https://sft.its.cern.ch/jira/browse/ROOT-8927

Same as with CEF, X still initialized

See https://reviews.llvm.org/D33366 for more.

See https://reviews.llvm.org/D34510 for more.

See https://reviews.llvm.org/D35536 for more.

Used in CEF batch and gui mode for direct communication between server
(ROOT7 canvas) and client (JSROOT code). Replaces websocket and
longpoll.

derived SimpleHandler from BaseHandler

It is base class, derived from CefClient, which mainly should handle 
messaging between JS client and web canvas. Such communication required
both in GUI and off-screen mode

Instead of longpoll protocol one can use CEF messaging, which allows to
send data directly to JS client from any place of the server. Messaging
callback initialized with first cefQuery, which made permanent

WS emulator submits same kind of requests to http server,
but engine created outside the server
Used for emulation of web sockets with CEF messaging functions.

Allow to copy data in provided buffer
Should care about additional byte, used as null-termination when data
used as plain string