Work around Closure Compiler bug to avoid upcoming type error

[lauraharker]

Fixing a compiler type equality bug uncovers a new error caused by https://github.com/google/closure-compiler/issues/2928.

third_party/javascript/polymer/v2/polymer/lib/utils/templatize.js:409: ERROR - [JSC_TYPE_MISMATCH] mismatch in declaration of superclass type found : templatizedBase required: templatizedBase class TemplatizedTemplateExtension extends templatizedBase {}; ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

(The found and required types are actually different classes completely, as the compiler is attaching the wrong type to TemplatizedTemplateExtension).

[lauraharker]

@rictic

This mirrors the Google-internal http://cl/268099757

[kevinpschaaf]

Noting that gen-typescript-declarations failed on CI:

lib/utils/templatize.d.ts:95:43 - error TS2552: Cannot find name 'templatizedBase'. Did you mean 'templatizerBase'?
95 declare class TemplatizedTemplate extends templatizedBase {
                                             ~~~~~~~~~~~~~~~
  lib/utils/templatize.d.ts:89:15
    89 declare class templatizerBase extends TemplateInstanceBase {
                     ~~~~~~~~~~~~~~~
    'templatizerBase' is declared here.
lib/utils/templatize.d.ts:101:52 - error TS2552: Cannot find name 'templatizedBase'. Did you mean 'templatizerBase'?
101 declare class TemplatizedTemplateExtension extends templatizedBase {
                                                       ~~~~~~~~~~~~~~~
  lib/utils/templatize.d.ts:89:15
    89 declare class templatizerBase extends TemplateInstanceBase {
                     ~~~~~~~~~~~~~~~
    'templatizerBase' is declared here.

[kevinpschaaf]

Thanks for the PR!