xdg-settings: add secondary check in GetIsDefaultWebClient

This CL fixes an issue where Chrome would display a banner saying that it
was not the default browser when it actually was.

The cause of this was 'xdg-settings check default-web-browser
google-chrome.desktop' returning 'no' when Chrome might have been the
default (see further explanation in the CL comments).

BUG=578888
R=thestig@chromium.org

Review-Url: https://codereview.chromium.org/2737283002
Cr-Commit-Position: refs/heads/master@{#456224}

chrome/browser/shell_integration_linux.cc

@@ -164,27 +164,26 @@ bool SetDefaultWebClient(const std::string& protocol) {
 #endif
 }
 
-// If |protocol| is empty this function checks if Chrome is the default browser,
-// otherwise it checks if Chrome is the default handler application for
-// |protocol|.
-DefaultWebClientState GetIsDefaultWebClient(const std::string& protocol) {
-#if defined(OS_CHROMEOS)
-  return UNKNOWN_DEFAULT;
-#else
-  base::ThreadRestrictions::AssertIOAllowed();
-
-  std::unique_ptr<base::Environment> env(base::Environment::Create());
-
+#if !defined(OS_CHROMEOS)
+// If |check| is true, returns the output of "xdg-settings check {property}
+// *.desktop", otherwise returns the output of "xdg-settings get {property}",
+// where property is "default-web-browser" if |protocol| is empty or
+// "default-url-scheme-handler |protocol|" otherwise.  Returns "" if
+// xdg-settings fails for any reason.
+std::string GetXdgSettingsOutput(bool check,
+                                 const std::string& protocol,
+                                 base::Environment* env) {
   std::vector<std::string> argv;
   argv.push_back(kXdgSettings);
-  argv.push_back("check");
+  argv.push_back(check ? "check" : "get");
   if (protocol.empty()) {
     argv.push_back(kXdgSettingsDefaultBrowser);
   } else {
     argv.push_back(kXdgSettingsDefaultSchemeHandler);
     argv.push_back(protocol);
   }
-  argv.push_back(shell_integration_linux::GetDesktopName(env.get()));
+  if (check)
+    argv.push_back(shell_integration_linux::GetDesktopName(env));
 
   std::string reply;
   int success_code;
@@ -197,15 +196,47 @@ DefaultWebClientState GetIsDefaultWebClient(const std::string& protocol) {
     }
   }
 
-  if (!ran_ok || success_code != EXIT_SUCCESS) {
-    // xdg-settings failed: we can't determine or set the default browser.
-    return UNKNOWN_DEFAULT;
+  if (!ran_ok || success_code != EXIT_SUCCESS)
+    return std::string();
+
+  return reply;
+}
+#endif
+
+// If |protocol| is empty this function checks if Chrome is the default browser,
+// otherwise it checks if Chrome is the default handler application for
+// |protocol|.
+DefaultWebClientState GetDefaultWebClient(const std::string& protocol) {
+#if defined(OS_CHROMEOS)
+  return UNKNOWN_DEFAULT;
+#else
+  base::ThreadRestrictions::AssertIOAllowed();
+
+  std::unique_ptr<base::Environment> env(base::Environment::Create());
+  std::string xdg_is_default = GetXdgSettingsOutput(true, protocol, env.get());
+  if (base::StartsWith(xdg_is_default, "yes", base::CompareCase::SENSITIVE)) {
+    return IS_DEFAULT;
+  }
+  if (base::StartsWith(xdg_is_default, "no", base::CompareCase::SENSITIVE)) {
+    // An output of "no" does not necessarily mean Chrom[e,ium] is not the
+    // default.  According to the xdg-settings man page, this can happen when
+    // "only some of the underlying settings actually reflect that value". Don't
+    // return NOT_DEFAULT unless we're sure, or else an annoying "Chrome is not
+    // your default browser" banner will appear on every launch
+    // (https://crbug.com/578888).
+    if (base::StartsWith(GetXdgSettingsOutput(false, protocol, env.get()),
+                         shell_integration_linux::GetDesktopName(env.get()),
+                         base::CompareCase::SENSITIVE)) {
+      // This is the odd case where 'xdg-settings check' said that Chrome wasn't
+      // the default, but 'xdg-settings get' returned Chrome as the default.
+      return UNKNOWN_DEFAULT;
+    }
+    // xdg-settings says the default is non-Chrome, and is self-consistent.
+    return NOT_DEFAULT;
   }
 
-  // Allow any reply that starts with "yes".
-  return base::StartsWith(reply, "yes", base::CompareCase::SENSITIVE)
-             ? IS_DEFAULT
-             : NOT_DEFAULT;
+  // xdg-settings failed: we can't determine or set the default browser.
+  return UNKNOWN_DEFAULT;
 #endif
 }
 
@@ -243,7 +274,7 @@ base::string16 GetApplicationNameForProtocol(const GURL& url) {
 }
 
 DefaultWebClientState GetDefaultBrowser() {
-  return GetIsDefaultWebClient(std::string());
+  return GetDefaultWebClient(std::string());
 }
 
 bool IsFirefoxDefaultBrowser() {
@@ -259,7 +290,7 @@ bool IsFirefoxDefaultBrowser() {
 }
 
 DefaultWebClientState IsDefaultProtocolClient(const std::string& protocol) {
-  return GetIsDefaultWebClient(protocol);
+  return GetDefaultWebClient(protocol);
 }
 
 }  // namespace shell_integration