Add ability to wire up sharelist in glcontext creation

src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp

Index: src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
diff --git a/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp b/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
index 41585c8632ece4da3b1cfc5ccdcaa0e69853d93c..9aa424d79b6c6d25aa689f119f7b3cf249502ab3 100644
--- a/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
+++ b/src/gpu/gl/mac/SkCreatePlatformGLContext_mac.cpp
@@ -109,7 +109,7 @@ GrGLFuncPtr MacGLContext::onPlatformGetProcAddress(const char* procName) const {
 
 } // anonymous namespace
 
-SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI) {
+SkGLContext* SkCreatePlatformGLContext(GrGLStandard forcedGpuAPI, SkGLContext*) {

[bsalomon, 2016/01/19 22:00:57]

I think these backends where it is unimplemented should fail if the sharedList
is non-null since the result would be surprising.

[joshualitt, 2016/01/20 14:36:56]

Acknowledged.

     if (kGLES_GrGLStandard == forcedGpuAPI) {
         return nullptr;
     }