Support multiple null GL contexts on a thread.

include/gpu/gl/SkNullGLContext.h

Index: include/gpu/gl/SkNullGLContext.h
diff --git a/src/gpu/gl/SkNullGLContext.h b/include/gpu/gl/SkNullGLContext.h
similarity index 53%
rename from src/gpu/gl/SkNullGLContext.h
rename to include/gpu/gl/SkNullGLContext.h
index b0432ba2e64c36d32b5f9f0ccc365d791037bf22..1715cfe597956875d70069eb4fc3655cea1389f8 100644
--- a/src/gpu/gl/SkNullGLContext.h
+++ b/include/gpu/gl/SkNullGLContext.h
@@ -13,23 +13,17 @@
 class SK_API SkNullGLContext : public SkGLContext {
 public:
     ~SkNullGLContext() SK_OVERRIDE;
-    void makeCurrent() const SK_OVERRIDE {};
+    void makeCurrent() const SK_OVERRIDE;
     void swapBuffers() const SK_OVERRIDE {};
 
-    static SkNullGLContext* Create(GrGLStandard forcedGpuAPI) {
-        if (kGLES_GrGLStandard == forcedGpuAPI) {
-            return NULL;
-        }
-        SkNullGLContext* ctx = SkNEW(SkNullGLContext);
-        if (!ctx->isValid()) {
-            SkDELETE(ctx);
-            return NULL;
-        }
-        return ctx;
-    }
+    static SkNullGLContext* Create(GrGLStandard);
+
+    struct ContextState;
 
 private:
     SkNullGLContext();
+
+    ContextState* fState;
 };
 
 #endif