Use stub GL draw/clear calls for browser tests that do not need pixels.

ui/gl/gl_implementation.cc

Index: ui/gl/gl_implementation.cc
diff --git a/ui/gl/gl_implementation.cc b/ui/gl/gl_implementation.cc
index d8de8c26913c24ee4c96a45ff1533bfc63a38a62..aae4bdd7da2b7ddceb52979b393c492a2abdefa9 100644
--- a/ui/gl/gl_implementation.cc
+++ b/ui/gl/gl_implementation.cc
@@ -11,6 +11,7 @@
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "ui/gl/gl_bindings.h"
+#include "ui/gl/gl_gl_api_implementation.h"
 
 namespace gfx {
 
@@ -171,4 +172,10 @@ void* GetGLProcAddress(const char* name) {
   return proc;
 }
 
+void InitializeStubGLBindings() {
+  // Only the GL library has stubbed out methods, and this is
+  // platform-independent.
+  InitializeStubGLBindingsGL();
+}
+
 }  // namespace gfx