Fix cppcheck warnings (#11883)

* remove unused variable

* limit scope of variable 'ret'

* pass shared_ptr<SkBitmap> by reference

* silence warning: value reassign before read

* fix oops

* don't refer to 'response' after std::move()ing it

* make the linter happy

atom/browser/atom_browser_main_parts_posix.cc

@@ -119,9 +119,8 @@ void ShutdownDetector::ThreadMain() {
 
   int signal;
   size_t bytes_read = 0;
-  ssize_t ret;
   do {
-    ret = HANDLE_EINTR(
+    ssize_t ret = HANDLE_EINTR(
         read(shutdown_fd_,
              reinterpret_cast<char*>(&signal) + bytes_read,
              sizeof(signal) - bytes_read));

atom/browser/atom_web_ui_controller_factory.cc

@@ -52,7 +52,7 @@ AtomWebUIControllerFactory::CreateWebUIControllerForURL(content::WebUI* web_ui,
   if (url.host() == kPdfViewerUIHost) {
     base::StringPairs toplevel_params;
     base::SplitStringIntoKeyValuePairs(url.query(), '=', '&', &toplevel_params);
-    std::string stream_id, src;
+    std::string src;
 
     const net::UnescapeRule::Type unescape_rules =
       net::UnescapeRule::SPACES | net::UnescapeRule::PATH_SEPARATORS |

atom/browser/osr/osr_render_widget_host_view.cc

@@ -194,7 +194,7 @@ class AtomCopyFrameGenerator {
 
   void OnCopyFrameCaptureSuccess(
       const gfx::Rect& damage_rect,
-      std::shared_ptr<SkBitmap> bitmap) {
+      const std::shared_ptr<SkBitmap>& bitmap) {
     base::AutoLock lock(onPaintLock_);
     view_->OnPaint(damage_rect, *bitmap);
   }