Introduce GLStubApi

ui/gl/gl_gl_api_implementation.cc

Index: ui/gl/gl_gl_api_implementation.cc
diff --git a/ui/gl/gl_gl_api_implementation.cc b/ui/gl/gl_gl_api_implementation.cc
index 3ef10a54dc51cd73f82aa9c15d88535e3f1f98fa..9dbb29faac40b2a9d9507ed61c7ef00c610fdeb9 100644
--- a/ui/gl/gl_gl_api_implementation.cc
+++ b/ui/gl/gl_gl_api_implementation.cc
@@ -28,6 +28,8 @@ static RealGLApi* g_real_gl = NULL;
 static NoContextGLApi* g_no_context_gl = NULL;
 // A GL Api that calls TRACE and then calls another GL api.
 static TraceGLApi* g_trace_gl = NULL;
+// The GL Api being used for stub contexts. If null, g_gl is used instead.
+static GLApi* g_stub_gl = NULL;
 // GL version used when initializing dynamic bindings.
 static GLVersionInfo* g_version_info = NULL;
 
@@ -380,10 +382,18 @@ void SetGLToRealGLApi() {
   SetGLApi(g_gl);
 }
 
+void SetGLToStubGLApi() {
+  SetGLApi(g_stub_gl ? g_stub_gl : g_gl);

[no sievers, 2016/07/11 22:42:41]

What uses GLContextStub in a way that this has to fall back to the real API?

[piman, 2016/07/11 23:57:27]

The mock bindings use RealGLApi, but hooking GetProcAddress to return a
trampoline function that calls into the MockGLInterface. I suspect it would be
possible to change the mock bindings to also hook directly at the GLApi level
instead (a little saner), but there is so much test code that relies on the
current hookup that I think it wouldn't be productive to try to migrate it
wholesale.

+}
+
 void SetGLApiToNoContext() {
   SetGLApi(g_no_context_gl);
 }
 
+void SetStubGLApi(GLApi* api) {
+  g_stub_gl = api;
+}
+
 const GLVersionInfo* GetGLVersionInfo() {
   return g_version_info;
 }
@@ -430,6 +440,7 @@ void ClearGLBindingsGL() {
     g_no_context_gl = NULL;
   }
   g_gl = NULL;
+  g_stub_gl = NULL;
   g_driver_gl.ClearBindings();
   if (g_current_gl_context_tls) {
     delete g_current_gl_context_tls;