Abstract OSMesa from the Layout tests

ui/gl/gl_implementation.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // 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_H_
 #define UI_GL_GL_IMPLEMENTATION_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 61 matching lines @@
  private:
   bool initial_enabled_;
 };
 
 // Set the current GL implementation.
 GL_EXPORT void SetGLImplementation(GLImplementation implementation);
 
 // Get the current GL implementation.
 GL_EXPORT GLImplementation GetGLImplementation();
 
+// Get the software GL implementation for the current platform.
+GL_EXPORT GLImplementation GetSoftwareGLImplementation();
+
 // Does the underlying GL support all features from Desktop GL 2.0 that were
 // removed from the ES 2.0 spec without requiring specific extension strings.
 GL_EXPORT bool HasDesktopGLFeatures();
 
 // Get the GL implementation with a given name.
 GL_EXPORT GLImplementation GetNamedGLImplementation(const std::string& name);
 
 // Get the name of a GL implementation.
 GL_EXPORT const char* GetGLImplementationName(GLImplementation implementation);
 
@@ skipping 35 matching lines @@
 
 // Helpers to load a library and log error on failure.
 GL_EXPORT base::NativeLibrary LoadLibraryAndPrintError(
     const base::FilePath::CharType* filename);
 GL_EXPORT base::NativeLibrary LoadLibraryAndPrintError(
     const base::FilePath& filename);
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_IMPLEMENTATION_H_