Migrate WTF::HashMap::get() to ::at()

third_party/WebKit/Source/core/frame/csp/SourceListDirective.cpp

Index: third_party/WebKit/Source/core/frame/csp/SourceListDirective.cpp
diff --git a/third_party/WebKit/Source/core/frame/csp/SourceListDirective.cpp b/third_party/WebKit/Source/core/frame/csp/SourceListDirective.cpp
index c53f5b901e4756ae556f01fd316ae05e9a26ea58..0a81bf5eac573291ba8cb145ce3b09a3b6648331 100644
--- a/third_party/WebKit/Source/core/frame/csp/SourceListDirective.cpp
+++ b/third_party/WebKit/Source/core/frame/csp/SourceListDirective.cpp
@@ -767,9 +767,9 @@ SourceListDirective::getIntersectSchemesOnly(
       if (schemesA.contains(sourceB->getScheme()))
         addSourceToMap(intersect, sourceB);
       else if (sourceB->getScheme() == "http" && schemesA.contains("https"))
-        intersect.insert("https", schemesA.get("https"));
+        intersect.insert("https", schemesA.at("https"));
       else if (sourceB->getScheme() == "ws" && schemesA.contains("wss"))
-        intersect.insert("wss", schemesA.get("wss"));
+        intersect.insert("wss", schemesA.at("wss"));
     }
   }