Make it possible to use OSMesa on Android

ui/gl/gl_implementation_osmesa.h

Index: ui/gl/gl_implementation_osmesa.h
diff --git a/ui/gl/gl_implementation_linux.h b/ui/gl/gl_implementation_osmesa.h
similarity index 77%
rename from ui/gl/gl_implementation_linux.h
rename to ui/gl/gl_implementation_osmesa.h
index 1c32d4cbf6573e78dc0e2483b295c1ebf21c18b5..dbf6bba20a2fccb1d056f96d3538258db5986a3e 100644
--- a/ui/gl/gl_implementation_linux.h
+++ b/ui/gl/gl_implementation_osmesa.h
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef UI_GL_GL_IMPLEMENTATION_OSMESA_
+#define UI_GL_GL_IMPLEMENTATION_OSMESA_
+
 #include "base/files/file_path.h"
 #include "base/native_library.h"
 
@@ -12,3 +15,5 @@ base::NativeLibrary LoadLibrary(const char* filename);
 base::NativeLibrary LoadLibrary(const base::FilePath& filename);
 
 }  // namespace gfx
+
+#endif  // UI_GL_GL_IMPLEMENTATION_OSMESA_