Ensure GL initialization only happens once, and provide common init path

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 <string>
 #include <vector>
 
@@ skipping 24 matching lines @@
 
 void GetAllowedGLImplementations(std::vector<GLImplementation>* impls);
 
 #if defined(OS_WIN)
 typedef void* (WINAPI *GLGetProcAddressProc)(const char* name);
 #else
 typedef void* (*GLGetProcAddressProc)(const char* name);
 #endif
 
 // Initialize a particular GL implementation.
-GL_EXPORT bool InitializeStaticGLBindings(GLImplementation implementation);
+bool InitializeStaticGLBindings(GLImplementation implementation);
 
 // Initialize function bindings that depend on the context for a GL
 // implementation.
-GL_EXPORT bool InitializeDynamicGLBindings(GLImplementation implementation,
-    GLContext* context);
+bool InitializeDynamicGLBindings(GLImplementation implementation,
+                                 GLContext* context);
 
 // Initialize Debug logging wrappers for GL bindings.
 void InitializeDebugGLBindings();
 
 // Initialize stub methods for drawing operations in the GL bindings.
 void InitializeNullDrawGLBindings();
 
-GL_EXPORT void ClearGLBindings();
+void ClearGLBindings();
 
 // Set the current GL implementation.
 GL_EXPORT void SetGLImplementation(GLImplementation implementation);
 
 // Get the current GL implementation.
 GL_EXPORT GLImplementation GetGLImplementation();
 
 // 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();
@@ skipping 22 matching lines @@
 // unsupported.
 void* GetGLProcAddress(const char* name);
 
 // Return information about the GL window system binding implementation (e.g.,
 // EGL, GLX, WGL). Returns true if the information was retrieved successfully.
 GL_EXPORT bool GetGLWindowSystemBindingInfo(GLWindowSystemBindingInfo* info);
 
 }  // namespace gfx
 
 #endif  // UI_GL_GL_IMPLEMENTATION_H_