https://bugs.webkit.org/show_bug.cgi?id=86037

Reviewed by Alejandro G. Castro.

Source/WebCore:

No new tests. These changes are covered by the compositing tests, which
we will gradually try to turn on for the bots.

Add a new GLContext method for getting to current default framebuffer size, which
is quite useful for preventing composited content quivering while resizing.

* platform/graphics/cairo/GLContext.h:
* platform/graphics/glx/GLContextGLX.cpp:
(WebCore::GLContextGLX::defaultFrameBufferSize): Added this implementation for X11
which asks the X server for the window size.
* platform/graphics/glx/GLContextGLX.h:

Source/WebKit2:

Add an implementation of LayerTreeHost for GTK+ that uses TextureMapperGL.
Later this implementation will fall back to using the ImageBuffer TextureMapper.

* GNUmakefile.am: Add new files to the compilation.
* Shared/LayerTreeContext.h:
(LayerTreeContext): The GTK+ version of the LayerTreeContext just holds window handle.
* Shared/gtk/LayerTreeContextGtk.cpp: Copied from Source/WebKit2/WebProcess/WebPage/LayerTreeHost.cpp.
* WebProcess/WebPage/gtk/LayerTreeHostGtk.h: Added.
* WebProcess/WebPage/gtk/LayerTreeHostGtk.cpp: Added.
Add this LayerTreeHost implementation that just creates a GL context from the widget X11 window ID.
Later implementations might find a more cross-platform solution.
* WebProcess/WebPage/gtk/WebPageGtk.cpp:
(WebKit::WebPage::platformInitialize): Initialize the native window handle to be zero.
(WebKit::WebPage::widgetMapped): When mapping the widget, try to get the native window
handle and send it to the WebProcess.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@120262 268f45cc-cd09-0410-ab3c-d52691b4dbfc