Default to 'never' referrer policy for invalid meta tags on iOS.

The w3c spec indicates that parsing an unsupported value for referrer
meta tags should not result in a referrer policy change.  However, when
WKWebView detects one of these tags, it will change the policy to
'never'.

testWebReferrerOpenInNewTab verifies this observed behavior of WKWebView
but https://codereview.chromium.org/2918313002/ updated
ReferrerPolicyFromString() to assume strict adherance to the latest spec
rather than WKWebView's actual implementation.  This change updates the
context menu param construction to use 'never' for unsupported referrer
meta tag values so that the policy is consistently defaulted to 'never'
for pages that are opened in a new Tab.

w3c spec: https://w3c.github.io/webappsec-referrer-policy/#unknown-policy-values

Bug: 733202
Change-Id: I74772f799a78c726601debddf64dd8f9ebbb2e0e
Reviewed-on: https://chromium-review.googlesource.com/580630
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488810}

ios/web/web_state/js/context_menu_js_unittest.mm

@@ -224,4 +224,19 @@ TEST_F(ContextMenuJsTest, LinkOfImageWithCalloutNone) {
   EXPECT_NSEQ(expected_result, result);
 }
 
+// Tests that the GetElementFromPoint script reports "never" as the referrer
+// policy for pages that have an unsupported policy in a meta tag.
+TEST_F(ContextMenuJsTest, UnsupportedReferrerPolicy) {
+  // A page with an unsupported referrer meta tag and a 400x400 image.
+  static const char kInvalidReferrerTag[] =
+      "<meta name=\"referrer\" content=\"unsupported-value\">"
+      "<img width=400 height=400 src='foo'></img>";
+
+  // Load the invalid meta tag
+  LoadHtml(kInvalidReferrerTag);
+  id result = ExecuteGetElementFromPointJavaScript(20, 20);
+  ASSERT_TRUE([result isKindOfClass:[NSDictionary class]]);
+  EXPECT_NSEQ(@"never", result[kContextMenuElementReferrerPolicy]);
+}
+
 }  // namespace web

ios/web/web_state/js/resources/context_menu.js

@@ -279,10 +279,21 @@ goog.provide('__crWeb.contextMenu');
       }
     }
 
+    // Search for referrer meta tag.  WKWebView only supports a subset of values
+    // for referrer meta tags.  If it parses a referrer meta tag with an
+    // unsupported value, it will default to 'never'.
     var metaTags = document.getElementsByTagName('meta');
     for (var i = 0; i < metaTags.length; ++i) {
       if (metaTags[i].name.toLowerCase() == 'referrer') {
-        return metaTags[i].content.toLowerCase();
+        var referrerPolicy = metaTags[i].content.toLowerCase();
+        if (referrerPolicy == 'no-referrer' ||
+            referrerPolicy == 'orgin' ||
+            referrerPolicy == 'no-referrer-when-downgrade' ||
+            referrerPolicy == 'unsafe-url') {
+          return referrerPolicy;
+        } else {
+          return 'never';
+        }
       }
     }
     return 'default';