Add ability to wire up sharelist in glcontext creation

src/gpu/gl/egl/SkCreatePlatformGLContext_egl.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"
 
 #include <GLES2/gl2.h>
@@ skipping 299 matching lines @@
                                                                EGL_FOREVER_KHR);
 }
 
 void SkEGLFenceSync::deleteFence(SkPlatformGpuFence platformFence) const {
     EGLSyncKHR eglsync = static_cast<EGLSyncKHR>(platformFence);
     eglDestroySyncKHR(fDisplay, eglsync);
 }
 
 } // anonymous namespace
 
-SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI) {
+SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI, SkGLContext* shareContext) {
+    SkASSERT(!shareContext);

[bsalomon, 2016/01/20 15:26:07]

Why these asserts rather than just return nullptr?

[joshualitt, 2016/01/20 15:45:20]

I can see it both ways.  It make it easier to spot the failure because the
program will halt at the offending line, instead of just getting a null context
and not knowing why.  Also, I didn't want to clutter up all of these functions
with an additional check.

Of course, this means it won't work in release builds, which is unfortunate.

If you have a preference for returning null, then I can go that route.

     EGLGLContext* ctx = new EGLGLContext(forcedGpuAPI);
     if (!ctx->isValid()) {
         delete ctx;
         return nullptr;
     }
     return ctx;
 }