Support DXT textures with non-block sized mip levels.

The block size requirement for each mip level meant that all
DXT textures had to be POT sized. Relax these restrictions for
non-zero mip levels to allow NPOT DXT textures.

Bug: angleproject:4841
Change-Id: I6d5cde0c9eec220d9d82a73fc069743d3a934746
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2416748Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808427}

gpu/command_buffer/service/gl_utils.cc

@@ -47,11 +47,9 @@ bool IsValidPVRTCSize(GLint level, GLsizei size) {
 }
 
 bool IsValidS3TCSizeForWebGLAndANGLE(GLint level, GLsizei size) {
-  // WebGL and ANGLE only allow multiple-of-4 sizes, except for levels > 0 where
-  // it also allows 1 or 2. See WEBGL_compressed_texture_s3tc and
-  // ANGLE_compressed_texture_dxt*
-  return (level && size == 1) || (level && size == 2) ||
-         !(size % kS3TCBlockWidth);
+  // WebGL and ANGLE only allow multiple-of-4 sizes for the base level. See
+  // WEBGL_compressed_texture_s3tc and ANGLE_compressed_texture_dxt*
+  return (level > 0) || (size % kS3TCBlockWidth == 0);
 }
 
 const char* GetDebugSourceString(GLenum source) {