[SystemInfo API] Rewrite DisplayInfoProvider without SystemInfoProvider.

chrome/browser/extensions/api/system_display/display_info_provider.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/api/system_display/display_info_provider.h"
 
+#include "base/lazy_instance.h"
 #include "base/strings/string_number_conversions.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/screen.h"
 
 namespace extensions {
 
 namespace {
 
 // Converts Rotation enum to integer.
 int RotationToDegrees(gfx::Display::Rotation rotation) {
   switch (rotation) {
     case gfx::Display::ROTATE_0:
       return 0;
     case gfx::Display::ROTATE_90:
       return 90;
     case gfx::Display::ROTATE_180:
       return 180;
     case gfx::Display::ROTATE_270:
       return 270;
   }
   return 0;
 }
 
-// Creates new DisplayUnitInfo struct for |display| and adds it at the end of
-// |list|.
+// Creates new DisplayUnitInfo struct for |display|.
 extensions::api::system_display::DisplayUnitInfo*
-CreateDisplayUnitInfo(const gfx::Display& display,
-               int64 primary_display_id) {
+CreateDisplayUnitInfo(const gfx::Display& display, int64 primary_display_id) {
   extensions::api::system_display::DisplayUnitInfo* unit =
       new extensions::api::system_display::DisplayUnitInfo();
   const gfx::Rect& bounds = display.bounds();
   const gfx::Rect& work_area = display.work_area();
   unit->id = base::Int64ToString(display.id());
   unit->is_primary = (display.id() == primary_display_id);
   unit->is_internal = display.IsInternal();
   unit->is_enabled = true;
   unit->rotation = RotationToDegrees(display.rotation());
   unit->bounds.left = bounds.x();
   unit->bounds.top = bounds.y();
   unit->bounds.width = bounds.width();
   unit->bounds.height = bounds.height();
   unit->work_area.left = work_area.x();
   unit->work_area.top = work_area.y();
   unit->work_area.width = work_area.width();
   unit->work_area.height = work_area.height();
   return unit;
 }
 
 }  // namespace
 
-DisplayInfoProvider::DisplayInfoProvider() {
-}
+static base::LazyInstance<scoped_ptr<DisplayInfoProvider> >
+  g_display_info_provider = LAZY_INSTANCE_INITIALIZER;

[oshima, 2013/09/06 18:30:48]

Given that you instantiate new object yourself, there is no need
to use LazyInstance.

Just use

DisplayInfoProvider* display_info_provider = NULL; (g_ prefix is optional and up
to you)

in anonymous namespace in this file.

[Haojian Wu, 2013/09/07 03:16:53]

One big concern: if we use the raw global pointer instead of C++ RAII
technology, I think it's hard to safely maintain the pointer's lifttime(such as.
when to delete it?)

Any suggestion about it? Maybe we can put this pointer into DisplayInfoProvider
class.

 
-DisplayInfoProvider::~DisplayInfoProvider() {
-}
+DisplayInfoProvider::DisplayInfoProvider() {}
 
-// Static member intialization.
-base::LazyInstance<scoped_refptr<DisplayInfoProvider > >
-    DisplayInfoProvider::provider_ = LAZY_INSTANCE_INITIALIZER;
+DisplayInfoProvider::~DisplayInfoProvider() {}
 
-const DisplayInfo& DisplayInfoProvider::display_info() const {
-  return info_;
+DisplayInfoProvider* DisplayInfoProvider::Get() {
+  if (g_display_info_provider.Get().get() == NULL)
+    g_display_info_provider.Get() = scoped_ptr<DisplayInfoProvider>(
+        new DisplayInfoProvider);
+  return g_display_info_provider.Get().get();
 }
 
 void DisplayInfoProvider::InitializeForTesting(
-    scoped_refptr<DisplayInfoProvider> provider) {
-  DCHECK(provider.get() != NULL);
-  provider_.Get() = provider;
+    DisplayInfoProvider* display_info_provider) {
+  g_display_info_provider.Get() = scoped_ptr<DisplayInfoProvider>(
+      display_info_provider);
 }
 
-void DisplayInfoProvider::RequestInfo(const RequestInfoCallback& callback) {
-  bool success = QueryInfo();
-
-  base::MessageLoopProxy::current()->PostTask(
-      FROM_HERE,
-      base::Bind(callback, success));
-}
-
-#if !defined(OS_WIN)
-bool DisplayInfoProvider::QueryInfo() {
-  info_.clear();
-
+DisplayInfo DisplayInfoProvider::GetAllDisplaysInfo() {
   // TODO(scottmg): Native is wrong http://crbug.com/133312
   gfx::Screen* screen = gfx::Screen::GetNativeScreen();
   int64 primary_id = screen->GetPrimaryDisplay().id();
   std::vector<gfx::Display> displays = screen->GetAllDisplays();
+  DisplayInfo all_displays;
   for (int i = 0; i < screen->GetNumDisplays(); ++i) {
     linked_ptr<extensions::api::system_display::DisplayUnitInfo> unit(
         CreateDisplayUnitInfo(displays[i], primary_id));
     UpdateDisplayUnitInfoForPlatform(displays[i], unit.get());
-    info_.push_back(unit);
+    all_displays.push_back(unit);
   }
-  return true;
-}
-#endif
-
-// static
-DisplayInfoProvider* DisplayInfoProvider::Get() {
-  if (provider_.Get().get() == NULL)
-    provider_.Get() = new DisplayInfoProvider();
-  return provider_.Get();
+  return all_displays;
 }
 
 }  // namespace extensions