Revert "Disable ParameterizedShowActionDeclarativeContentApiTest.ActionInManifest"

This reverts commit 76a2b442.

Reason for revert: Disabling is non-actionable, see crbug.com/1010061#c11

Original change's description:
> Disable ParameterizedShowActionDeclarativeContentApiTest.ActionInManifest
> 
> TBR=jyasskin@chromium.org
> NOTRY=true
> 
> Bug: 1010061
> Change-Id: I741e49ba958631aa46dd9a77995a5060ce12b200
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1832913
> Reviewed-by: Xida Chen <xidachen@chromium.org>
> Commit-Queue: Xida Chen <xidachen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#701620}

TBR=jyasskin@chromium.org,xidachen@chromium.org

Change-Id: I1687b2e180c961ab43d5e016061355539add39ad
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1010061
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1834185Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701922}

chrome/browser/extensions/api/declarative_content/declarative_content_apitest.cc

@@ -534,9 +534,8 @@ IN_PROC_BROWSER_TEST_P(ParameterizedShowActionDeclarativeContentApiTest,
   TestShowAction(ActionInfo::TYPE_BROWSER);
 }
 
-// crbug.com/1010061: disabled due to flakiness.
 IN_PROC_BROWSER_TEST_P(ParameterizedShowActionDeclarativeContentApiTest,
-                       DISABLED_ActionInManifest) {
+                       ActionInManifest) {
   TestShowAction(ActionInfo::TYPE_ACTION);
 }