[AW] Fix //aw/gpu/DEPS

crrev.com/c/1954543 was missing an include rule in //aw/gpu/DEPS.

TBR=torne@chromium.org

Test: buildtools/checkdeps/checkdeps.py android_webview
Bug: 1031659
Change-Id: I943106937f674cc6967a9f8b8f69d7711a3cfc33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1956068Reviewed-by: Robbie McElrath <rmcelrath@chromium.org>
Commit-Queue: Robbie McElrath <rmcelrath@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722615}

android_webview/gpu/DEPS

@@ -2,5 +2,6 @@ include_rules = [
   "-android_webview",
   "+android_webview/common",
   "+android_webview/common_jni_headers",
+  "+android_webview/gpu",
   "+content/public/gpu",
 ]