Added Client-Hints.

chrome/browser/net/client_hints.cc

+// Copyright (c) 2012 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/net/client_hints.h"
+
+#include "base/stringprintf.h"
+#include "content/public/browser/browser_thread.h"
+#include "ui/gfx/screen.h"
+
+using content::BrowserThread;
+
+ClientHints::ClientHints() : screen_hints_("") {
+}
+
+ClientHints::~ClientHints() {
+}
+
+bool ClientHints::RetrieveScreenInfo() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  return BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
+      base::Bind(&ClientHints::FetchScreenInfoOnUIThread, this));

[Ryan Sleevi, 2013/02/08 22:12:53]

For example:

namespace {
typedef base::Callback<void(int, int, float)> ClientHintsCallback;

void FetchScreenInfoOnUIThread(const ClientHintsCallback& cb) {
  DCHECK(... ::UI));
  gfx::Display display = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
  cb.Run(display.GetSizeInPixel().width(),
         display.GetSizeInPixel().height(),
         display.device_scale_factor());
}

}

bool ClientHints::RetrieveScreenInfo() {
  DCHECK(... IO));
  ClientHintsCallback cb = 
      base::Bind(
          &BrowserThread::PostTask,
          BrowserThread::IO,
          FROM_HERE,
          base::Bind(&ClientHints::UpdateScreenInfo,
                     weak_ptr_factory_.GetWeakPtr()));
  return BrowserThread::PostTask(
    BrowserThread::UI, FROM_HERE,
    base::Bind(&FetchScreenInfoOnUIThread, cb));
}


No refcounting needed, and you still end up with 'safety'

The extra bind to PostTask could alternatively be done with
PostTaskAndReplyWithResult (which only handles one result value, not the three
you're using), but that actually ends up with even more indirection and either
exposing the struct publically or exposing the UpdateScreenInfo publicly, which
I wanted to avoid.

[bengr, 2013/02/26 01:57:20]

I couldn't get your suggestion to compile. I wound up using PostTaskAndReply and
replied with a struct. The struct is exposed as a public member of ClientHints.
I tried declaring it in an anonymous namespace, which worked fine for
client_hint.{h,cc}, but I got an odd error when I tried to build the tests:

In file included from ../../chrome/browser/net/client_hints_unittest.cc:5:
../../chrome/browser/net/client_hints.h:46:8: error: function
'ClientHints::UpdateScreenInfo' has internal linkage but is not defined
[-Werror,-Wundefined-internal]
  void UpdateScreenInfo(ScreenInfo* info);
       ^
../../chrome/browser/net/client_hints_unittest.cc:21:20: note: used here
    client_hints_->UpdateScreenInfo(&info);


On 2013/02/08 22:12:53, Ryan Sleevi wrote:

+}
+
+std::string ClientHints::GetScreenInfoHints() {
+  return screen_hints_;
+}
+
+void ClientHints::FetchScreenInfoOnUIThread() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  gfx::Display display = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
+  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
+      base::Bind(&ClientHints::UpdateScreenInfo, this,
+                 display.GetSizeInPixel().width(),
+                 display.GetSizeInPixel().height(),
+                 display.device_scale_factor()));
+}
+
+void ClientHints::UpdateScreenInfo(int width, int height,
+                                   float device_pixel_ratio) {
+  screen_hints_ = base::StringPrintf("dh=%d, dw=%d, dpr=%0.3g",
+                                     height, width, device_pixel_ratio);
+}
+