Make --install-chrome-app use extensions::WebstoreInstallWithPrompt.

chrome/browser/extensions/startup_helper.cc

Index: chrome/browser/extensions/startup_helper.cc
diff --git a/chrome/browser/extensions/startup_helper.cc b/chrome/browser/extensions/startup_helper.cc
index 4074b5f7c849ac6145256c68fb78777493b9e84e..66c8ff155e2e86465e37c38d57f19a63a74bbd40 100644
--- a/chrome/browser/extensions/startup_helper.cc
+++ b/chrome/browser/extensions/startup_helper.cc
@@ -264,6 +264,10 @@ void DeleteHelperAndRunCallback(AppInstallHelper* helper,
   callback.Run();
 }
 
+void DeleteHelper(AppInstallHelper* helper) {
+  delete helper;
+}
+
 }  // namespace
 
 bool StartupHelper::InstallFromWebstore(const CommandLine& cmd_line,
@@ -302,6 +306,21 @@ void StartupHelper::LimitedInstallFromWebstore(
                                   helper, done_callback));
 }
 
+void StartupHelper::InstallChromeApp(
+    const CommandLine& cmd_line,
+    Profile* profile) {
+  std::string id = cmd_line.GetSwitchValueASCII(switches::kInstallChromeApp);
+  if (!Extension::IdIsValid(id)) {

[tapted, 2014/07/25 03:49:12]

Would be nice to consolidate some of the repeated logic here... I guess they're
all just different enough though.

+    LOG(ERROR) << "Invalid id for " << switches::kInstallChromeApp
+               << " : '" << id << "'";
+    return;
+  }
+
+  AppInstallHelper* helper = new AppInstallHelper();
+  helper->BeginInstall(profile, id, true /*show_prompt*/,

[tapted, 2014/07/25 03:49:12]

Should the prompt that's shown be modal to a browser window? I don't think the
browser exists yet - how do you prevent the browser window covering up the
install prompt? (on Mac we hack the window layer, but I don't think that happens
with Views)

+                       base::Bind(&DeleteHelper, helper));
+}
+
 std::string StartupHelper::WebStoreIdFromLimitedInstallCmdLine(
     const CommandLine& cmd_line) {
   std::string index = cmd_line.GetSwitchValueASCII(