CMake: Compile in OSMesa on Linux, if found.

cmake/CMakeLists.txt

Index: cmake/CMakeLists.txt
diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 36a6d1ecf3ca947363c8197efebd4a2e5e82a64c..b0ec63fd49b4a17f6ce14d34706650701fc1a43a 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -100,7 +100,6 @@ remove_srcs(
     ../src/gpu/gl/command_buffer/*
     ../src/gpu/gl/egl/*
     ../src/gpu/gl/iOS/*
-    ../src/gpu/gl/mesa/*
     ../src/opts/SkBitmapProcState_opts_none.cpp
     ../src/opts/SkBlitMask_opts_none.cpp
     ../src/opts/SkBlitRow_opts_none.cpp
@@ -199,6 +198,15 @@ endif()
 find_package(OpenGL REQUIRED)
 list (APPEND libs  ${OPENGL_LIBRARIES})
 
+if (UNIX AND NOT APPLE AND EXISTS "/usr/include/GL/osmesa.h")

[mtklein, 2015/09/21 15:49:37]

Can you not do this like one of the other dependencies, either using
find_package (many examples) or find_path/find_library (webp, fontconfig)?

+    list (APPEND libs "OSMesa")
+    target_compile_definitions(skia
+        PUBLIC  -DSK_MESA
+        PRIVATE -DSK_MESA)
+else()
+    remove_srcs(../src/gpu/gl/mesa/*)
+endif()
+
 # This is our main output, libskia.so.
 # We mostly build an .so here because it helps test we've linked everything,
 # not so much that we think Skia is a good candidate to ship as a shared library.