Add ability to wire up sharelist in glcontext creation

src/gpu/gl/mac/SkCreatePlatformGLContext_mac.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 "SkTypes.h"
 #if defined(SK_BUILD_FOR_MAC)
 
@@ skipping 91 matching lines @@
 void MacGLContext::onPlatformSwapBuffers() const {
     CGLFlushDrawable(fContext);
 }
 
 GrGLFuncPtr MacGLContext::onPlatformGetProcAddress(const char* procName) const {
     return reinterpret_cast<GrGLFuncPtr>(dlsym(fGLLibrary, procName));
 }
 
 } // anonymous namespace
 
-SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI) {
+SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI, SkGLContext* shareContext) {
+    SkASSERT(!shareContext);
+    if (shareContext) {
+        return nullptr;
+    }
+
     if (kGLES_GrGLStandard == forcedGpuAPI) {
         return nullptr;
     }
     MacGLContext* ctx = new MacGLContext;
     if (!ctx->isValid()) {
         delete ctx;
         return nullptr;
     }
     return ctx;
 }
 
 #endif//defined(SK_BUILD_FOR_MAC)