Pass gl::Context to impl methods instead of ContextImpl.

In some cases we might have to call back into the GL layer, passing
the Context, and if we just have a ContextImpl pointer this isn't
possible. It also removes the need for SafeGetImpl.

BUG=angleproject:2044

Change-Id: I6363e84b25648c992c25779d4c43f795aa2866d6
Reviewed-on: https://chromium-review.googlesource.com/516835
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/VertexArray.cpp b/src/libANGLE/VertexArray.cpp
index b19e6ea..00d2180 100644
--- a/src/libANGLE/VertexArray.cpp
+++ b/src/libANGLE/VertexArray.cpp
@@ -218,7 +218,7 @@
 {
     if (mDirtyBits.any())
     {
-        mVertexArray->syncState(rx::SafeGetImpl(context), mDirtyBits);
+        mVertexArray->syncState(context, mDirtyBits);
         mDirtyBits.reset();
     }
 }