Adding user doc section and core files for new site

site/user/special/windows_angle.md

+Using ANGLE on Windows
+======================
+
+Introduction
+------------
+
+ANGLE converts OpenGL ES 2.0 calls to DirectX 9 calls. These instructions
+document how to use ANGLE instead of the native OpenGL backend on Windows.
+
+Details
+-------
+
+Angle is now downloaded as a part of Skia according to the `DEPS` file.
+
+Add `skia_angle=1` to your `GYP_DEFINES` environment variable.
+
+Run:
+
+    python gyp_skia
+
+Remember
+--------
+
+In SampleApp you will need to use the 'D' key to get to the ANGLE backend unless you enable the `DEFAULT_TO_ANGLE` #define in `SampleApp.cpp`.
+
+  * Use “--angle” to enable ANGLE in gm.
+
+  * Use “--config ANGLE” to use ANGLE in bench.
+
+  * Use "--config angle" to use ANGLE in bench_pictures and render_pictures.
+
+ANGLE will automatically be compiled into the GLInterfaceValidation test.