Workaround for Intel 6xxx clear to 0/1 bug

ui/gl/gl_context.h

Index: ui/gl/gl_context.h
diff --git a/ui/gl/gl_context.h b/ui/gl/gl_context.h
index 0d1aa6d0f40492d74e3f056cc3ffbd53e4a2ef74..9076c0a5306ca8721d7d4c799e88335be6981aea 100644
--- a/ui/gl/gl_context.h
+++ b/ui/gl/gl_context.h
@@ -68,11 +68,22 @@ struct GLContextAttribs {
   ContextPriority context_priority = ContextPriorityMedium;
 };
 
+struct GLWorkarounds {
+  // glClearColor does not always work on Intel 6xxx Mac drivers. See
+  // crbug.com/710443.
+  bool clear_to_zero_or_one_broken = false;
+};
+
 // Encapsulates an OpenGL context, hiding platform specific management.
 class GL_EXPORT GLContext : public base::RefCounted<GLContext> {
  public:
   explicit GLContext(GLShareGroup* share_group);
 
+  // Set the GL workarounds.
+  static void SetGLWorkarounds(const GLWorkarounds& workarounds);
+  // Get the GL workarounds.
+  static GLWorkarounds GetGLWorkarounds();
+
   // Initializes the GL context to be compatible with the given surface. The GL
   // context can be made with other surface's of the same type. The compatible
   // surface is only needed for certain platforms like WGL, OSMesa and GLX. It
@@ -222,6 +233,8 @@ class GL_EXPORT GLContext : public base::RefCounted<GLContext> {
 
   std::unique_ptr<GLVersionInfo> GenerateGLVersionInfo();
 
+  static GLWorkarounds gl_workarounds_;

[Zhenyao Mo, 2017/06/21 16:52:05]

Again, sorry for not being clear.  I think this needs to be a non-static member.
 Thinking about dual GPU situation, this really should be per context setting,
not a global setting.

[jiajia.qin, 2017/06/22 11:18:58]

OK. I have modified it to a non-static member. But a problem is that I need to
get the right context object in gl_gl_api_implementation.cc. Currently I added a
gl_context_ in RealGLApi like version_ did. Please check if it's the best method
to do it. 

+
   bool static_bindings_initialized_ = false;
   bool dynamic_bindings_initialized_ = false;
   std::unique_ptr<DriverGL> driver_gl_;