Add back dirty bits for pack / unpack buffer binding

BUG=angleproject:2169

Change-Id: I8cee9e1c7565d90022216d62b45f0eec5bc51f14
Reviewed-on: https://chromium-review.googlesource.com/755461
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/State.cpp b/src/libANGLE/State.cpp
index eca86b0..d56dcdc 100644
--- a/src/libANGLE/State.cpp
+++ b/src/libANGLE/State.cpp
@@ -1341,13 +1341,13 @@
 void State::setPixelPackBufferBinding(const Context *context, Buffer *buffer)
 {
     mPack.pixelBuffer.set(context, buffer);
-    mDirtyBits.set(DIRTY_BIT_PACK_STATE);
+    mDirtyBits.set(DIRTY_BIT_PACK_BUFFER_BINDING);
 }
 
 void State::setPixelUnpackBufferBinding(const Context *context, Buffer *buffer)
 {
     mUnpack.pixelBuffer.set(context, buffer);
-    mDirtyBits.set(DIRTY_BIT_UNPACK_STATE);
+    mDirtyBits.set(DIRTY_BIT_UNPACK_BUFFER_BINDING);
 }
 
 Buffer *State::getTargetBuffer(GLenum target) const