Make the webstore inline install dialog be tab-modal

Also clean up a few minor lint errors while I'm in here.

BUG=550047

Review URL: https://codereview.chromium.org/1496033003

Cr-Commit-Position: refs/heads/master@{#363925}
void ExtensionInstallPrompt::ConfirmWebstoreInstall(
    Delegate* delegate,
    const Extension* extension,
    const SkBitmap* icon,
    const ShowDialogCallback& show_dialog_callback) {
  extension_ = extension;
  SetIcon(icon);
  ConfirmInstall(delegate, extension, show_dialog_callback);
}

void ExtensionInstallPrompt::ConfirmWebstoreInstall(
    Delegate* delegate,
    const Extension* extension,
    const SkBitmap* icon,
    const ShowDialogCallback& show_dialog_callback) {
  extension_ = extension;
  SetIcon(icon);
  ConfirmInstall(delegate, extension, show_dialog_callback);
}
