Fix minor issues with ANGLE_texture_rectangle.

 * Some texture parameters were not initialized correctly.
 * Binding points were not created for enableable texture extensions.

BUG=angleproject:1650
BUG=angleproject:1523

Change-Id: Id3436fe1dbb4069eafad97e722ac519a6b59e5db
Reviewed-on: https://chromium-review.googlesource.com/744446
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index 022bf66..f6917f2 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -343,14 +343,15 @@
         }
     }
 
-    if (mExtensions.textureRectangle)
+    const Extensions &nativeExtensions = mImplementation->getNativeExtensions();
+    if (nativeExtensions.textureRectangle)
     {
         Texture *zeroTextureRectangle =
             new Texture(mImplementation.get(), 0, GL_TEXTURE_RECTANGLE_ANGLE);
         mZeroTextures[GL_TEXTURE_RECTANGLE_ANGLE].set(this, zeroTextureRectangle);
     }
 
-    if (mExtensions.eglImageExternal || mExtensions.eglStreamConsumerExternal)
+    if (nativeExtensions.eglImageExternal || nativeExtensions.eglStreamConsumerExternal)
     {
         Texture *zeroTextureExternal =
             new Texture(mImplementation.get(), 0, GL_TEXTURE_EXTERNAL_OES);