[ChromeDriver] Handle null capabilities

According to W3C spec, new session capabilities with null values should
be ignored, but they cause errors in ChromeDriver. This CL fixes it.

See https://www.w3.org/TR/webdriver/#dfn-validate-capabilities, step 3,
sub-steps 3 and 4.

Bug: chromedriver:1997
Change-Id: Ibee5e383c46139df1e5efc9f8a46872820c81046
Reviewed-on: https://chromium-review.googlesource.com/c/1340834
Commit-Queue: John Chen <johnchen@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609069}

chrome/test/chromedriver/capabilities.cc

@@ -761,6 +761,8 @@ Status Capabilities::Parse(const base::DictionaryValue& desired_caps,
 
   for (base::DictionaryValue::Iterator it(desired_caps); !it.IsAtEnd();
        it.Advance()) {
+    if (it.value().is_none())
+      continue;
     if (parser_map.find(it.key()) == parser_map.end()) {
       // The specified capability is unrecognized. W3C spec requires us to
       // return an error. In legacy mode, for backward compatibility reasons,

chrome/test/chromedriver/session_commands.cc

@@ -330,15 +330,15 @@ bool MergeCapabilities(const base::DictionaryValue* always_match,
   return true;
 }
 
+// Implementation of "matching capabilities", as defined in W3C spec at
+// https://www.w3.org/TR/webdriver/#dfn-matching-capabilities.
+// It checks some requested capabilities and make sure they are supported.
+// Currently, we only check "browserName", but more can be added as necessary.
 bool MatchCapabilities(const base::DictionaryValue* capabilities) {
-  // Attempt to match the capabilities requested to the actual capabilities.
-  // Reject if they don't match.
-  if (capabilities->HasKey("browserName")) {
-    std::string name;
-    capabilities->GetString("browserName", &name);
-    if (name != "chrome") {
+  const base::Value* name;
+  if (capabilities->Get("browserName", &name) && !name->is_none()) {
+    if (!(name->is_string() && name->GetString() == "chrome"))
       return false;
-    }
   }
   return true;
 }

chrome/test/chromedriver/session_commands_unittest.cc

@@ -151,6 +151,12 @@ TEST(SessionCommandsTest, ProcessCapabilities_AlwaysMatch) {
   std::string result_string;
   ASSERT_TRUE(result.GetString("browserName", &result_string));
   ASSERT_EQ(result_string, "chrome");
+
+  // Null "browserName" treated as not specifying "browserName"
+  params.SetPath({"capabilities", "alwaysMatch", "browserName"}, base::Value());
+  status = ProcessCapabilities(params, &result);
+  ASSERT_EQ(kOk, status.code()) << status.message();
+  ASSERT_FALSE(result.GetString("browserName", &result_string));
 }
 
 TEST(SessionCommandsTest, ProcessCapabilities_FirstMatch) {