Add ability to wire up sharelist in glcontext creation

src/gpu/gl/win/SkCreatePlatformGLContext_win.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/SkGLContext.h"
 
@@ skipping 169 matching lines @@
         SkDebugf("Could not complete SwapBuffers.\n");
     }
 }
 
 GrGLFuncPtr WinGLContext::onPlatformGetProcAddress(const char* name) const {
     return reinterpret_cast<GrGLFuncPtr>(wglGetProcAddress(name));
 }
 
 } // anonymous namespace
 
-SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI) {
+SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI, SkGLContext* shareContext) {
+    SkASSERT(!shareContext);
+    if (shareContext) {
+        return nullptr;
+    }
     WinGLContext* ctx = new WinGLContext(forcedGpuAPI);
     if (!ctx->isValid()) {
         delete ctx;
         return nullptr;
     }
     return ctx;
 }