Disable DevToolsExtensionTest.DevToolsExtensionSecurityPolicyGrants.

Flakiness dashboard:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=browser_tests&tests=DevToolsExtensionTest.DevToolsExtensionSecurityPolicyGrants

NOTRY=TRUE
TBR=dgozman@chromium.org

Bug: 993982
Change-Id: I1690e6db8ec7e6a67182075a45ce7891bc1bc2ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1760861Reviewed-by: Sahel Sharify <sahel@chromium.org>
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688110}

chrome/browser/devtools/devtools_sanity_browsertest.cc

@@ -1354,8 +1354,10 @@ IN_PROC_BROWSER_TEST_F(DevToolsSanityTest, DevtoolsInDevTools) {
 // Some web features, when used from an extension, are subject to browser-side
 // security policy enforcement. Make sure they work properly from inside a
 // devtools extension.
+// ToDo(993982): The test is flaky (timeout, crash, and fail) on several builds:
+// Debug, Windows, Mac, MSan, and ASan.
 IN_PROC_BROWSER_TEST_F(DevToolsExtensionTest,
-                       DevToolsExtensionSecurityPolicyGrants) {
+                       DISABLED_DevToolsExtensionSecurityPolicyGrants) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   auto dir = std::make_unique<extensions::TestExtensionDir>();