Fix GrGLSync definition

By fixing this some ugly casts are avoided in setting up Chrome's GrGLInterface

Change-Id: Ie540fc41b3cbb27f976d784cad90ae10c2cef9ed
Reviewed-on: https://skia-review.googlesource.com/12621
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/include/gpu/gl/GrGLTypes.h b/include/gpu/gl/GrGLTypes.h
index 0a2346e..f2b339e 100644
--- a/include/gpu/gl/GrGLTypes.h
+++ b/include/gpu/gl/GrGLTypes.h
@@ -60,7 +60,7 @@
 typedef signed long int GrGLsizeiptr;
 #endif
 typedef void* GrGLeglImage;
-typedef void* GrGLsync;
+typedef struct __GLsync* GrGLsync;
 
 struct GrGLDrawArraysIndirectCommand {
     GrGLuint fCount;