Invalidate completeness caches when enabling extensions.

Enabling extensions can cause framebuffers and textures to go from
incomplete to complete.

No functional changes from the API surface.

BUG=angleproject:1523
BUG=angleproject:1958

Change-Id: Iff686e1c292f6cf4921d6fffd7eb98bedaba828b
Reviewed-on: https://chromium-review.googlesource.com/468410
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/Framebuffer.h b/src/libANGLE/Framebuffer.h
index 9c5d128..a2d7606 100644
--- a/src/libANGLE/Framebuffer.h
+++ b/src/libANGLE/Framebuffer.h
@@ -188,6 +188,8 @@
     void setDefaultSamples(GLint defaultSamples);
     void setDefaultFixedSampleLocations(GLboolean defaultFixedSampleLocations);
 
+    void invalidateCompletenessCache();
+
     GLenum checkStatus(const Context *context);
 
     // TODO(jmadill): Remove this kludge.