Validate xoffset and yoffset are multiples of blocksize.

Affects glCompressedTexSubImage and glCopyCompressedTexSubImage calls.

BUG=668223

Change-Id: Ie71faa1fa7dac12cec51a2e29e0ce212ac54e411
Reviewed-on: https://chromium-review.googlesource.com/437605
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/libANGLE/validationES3.cpp b/src/libANGLE/validationES3.cpp
index 9754d5e..cf368e9 100644
--- a/src/libANGLE/validationES3.cpp
+++ b/src/libANGLE/validationES3.cpp
@@ -188,7 +188,8 @@
             return false;
         }
 
-        if (!ValidCompressedImageSize(context, actualInternalFormat, width, height))
+        if (!ValidCompressedImageSize(context, actualInternalFormat, xoffset, yoffset, width,
+                                      height))
         {
             context->handleError(Error(GL_INVALID_OPERATION));
             return false;