Add ability to wire up sharelist in glcontext creation

src/gpu/gl/iOS/SkCreatePlatformGLContext_iOS.mm

 
 /*
  * Copyright 2012 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"
 #import <OpenGLES/EAGL.h>
@@ skipping 71 matching lines @@
 }
 
 void IOSGLContext::onPlatformSwapBuffers() const { }
 
 GrGLFuncPtr IOSGLContext::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 NULL;
+    }
     if (kGL_GrGLStandard == forcedGpuAPI) {
         return NULL;
     }
     IOSGLContext* ctx = new IOSGLContext;
     if (!ctx->isValid()) {
         delete ctx;
         return NULL;
     }
     return ctx;
 }