[Net] Add a priority parameter to URLRequest's constructor

This is so that it is clearer what the intended initial priority of
a URLRequest is.

It is also needed so that we can later enforce that if a URLRequest
is set to ignore limits, it has MAXIMUM_PRIORITY; otherwise, we'd have
to mandate that SetPriority() is called before set_load_flags(), which
is fiddly.

Also standardize on a single URLRequest constructor.

BUG=166689
R=jam@chromium.org, jamesr@chromium.org, joth@chromium.org, mmenke@chromium.org, scottbyer@chromium.org, sky@chromium.org, tommi@chromium.org

Review URL: https://codereview.chromium.org/51953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232219 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232219
Split up hardware document into two documents: USB and serial.

STAGED DOCS:
https://chrome-apps-doc.appspot.com/_patch/38673005/apps/app_usb.html
https://chrome-apps-doc.appspot.com/_patch/38673005/apps/app_serial.html

R=mkearney@chromium.org

Review URL: https://codereview.chromium.org/38673005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232220 0039d316-1c4b-4281-b951-d872f2087c98
Revert 231597 "Fix extension/apps v2 compositing for software to..."

Breaks ppapi inside (I think) a webview tag.

> Fix extension/apps v2 compositing for software top-level
> 
> Causes the extension process to use a SoftwareOutputDevice
> rather than the gpu path, to go with https://src.chromium.org/viewvc/chrome?view=revision&revision=230981
> 
> R=wez@chromium.org, ananta@chromium.org
> BUG=312277
> 
> Review URL: https://codereview.chromium.org/48903011

TBR=scottmg@chromium.org
BUG=313462,313652

Review URL: https://codereview.chromium.org/51893004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232221 0039d316-1c4b-4281-b951-d872f2087c98
Blink roll 161057:161075

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=161058:161075&mode=html
TBR=
BUG=

Review URL: https://codereview.chromium.org/51763011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232222 0039d316-1c4b-4281-b951-d872f2087c98
[net/dns] Add support for DnsClient in MappedHostResolver.

All we have to do is forward the relevant methods to the wrapped impl_.

BUG=313455
R=mmenke@chromium.org

Review URL: https://codereview.chromium.org/53633002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232224 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232220
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232225 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232224
SVN changes up to revision 232225