Add ability to wire up sharelist in glcontext creation

src/gpu/gl/egl/SkCreatePlatformGLContext_egl.cpp

Index: src/gpu/gl/egl/SkCreatePlatformGLContext_egl.cpp
diff --git a/src/gpu/gl/egl/SkCreatePlatformGLContext_egl.cpp b/src/gpu/gl/egl/SkCreatePlatformGLContext_egl.cpp
index 3b2488dfc6ecba364f185d383c3eec4ff70708a4..821e0402617527272e769e440de096988995319b 100644
--- a/src/gpu/gl/egl/SkCreatePlatformGLContext_egl.cpp
+++ b/src/gpu/gl/egl/SkCreatePlatformGLContext_egl.cpp
@@ -317,7 +317,11 @@ void SkEGLFenceSync::deleteFence(SkPlatformGpuFence platformFence) const {
 
 } // anonymous namespace
 
-SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI) {
+SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI, SkGLContext* shareContext) {
+    SkASSERT(!shareContext);
+    if (shareContext) {
+        return nullptr;
+    }
     EGLGLContext* ctx = new EGLGLContext(forcedGpuAPI);
     if (!ctx->isValid()) {
         delete ctx;