Introduce a basic Blink Scheduler
    
This patch adds a bare-bones scheduler for prioritizing tasks that run
on the Blink main thread. The initial scheduling policy is to simply run
all tasks in their posted order.

The shared timer, WTF::callOnMainThread and by extension
WebCore::MainThreadTaskRunner are modified to route their tasks through
the Scheduler for eventual prioritization. A proxy for the scheduler is
also exposed in public/platform so that modules in content will be able
to post high priority (e.g., input and compositor-related) tasks.

Design document:
https://docs.google.com/a/chromium.org/document/d/11N2WTV3M0IkZ-kQlKWlBcwkOkKTCuLXGVNylK5E2zvc/edit#heading=h.3ay9sj44f0zd

BUG=391005
TEST=SchedulerTest.*

Review URL: https://codereview.chromium.org/364873002

git-svn-id: svn://svn.chromium.org/blink/trunk@178267 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Ensure that 'fetchMainResource' requests have a frame type.

This patch adds an ASSERT to 'ResourceFetcher::fetchMainResource' which
ensures that the request's FrameType is not FrameTypeNone, and uses that
information to ensure that the correct TargetType is synthesized when
heading back up into Chromium.

In order to make the ASSERT true, FrameLoader does a bit of work on the
NavigationAction it creates, and NavigationAction grows a
'mutableResourceRequest' method in order to allow that work to happen.

-----------------------------------------------------------------------
This is a re-land of r171181[1], reviewed in [2]. That CL was reverted,
as it hit an assert in a number of Chromium-side browser tests. This
iteration on the patch ensures that the FrameType is correctly set when
setting a WebURLRequest's TargetType.

[1]: https://src.chromium.org/viewvc/blink?view=rev&revision=178181
[2]: https://codereview.chromium.org/388253002/
-----------------------------------------------------------------------

BUG=390497
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/392203002

git-svn-id: svn://svn.chromium.org/blink/trunk@178268 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert of DevTools: Support async call stacks for FileSystem API (part 1). (https://codereview.chromium.org/383123009/)

Reason for revert:
This seems to add a lot of complexity into async code + violates the modularity: core/inspector should not be aware of the filesystems.

Original issue's description:
> DevTools: Support async call stacks for FileSystem API (part 1).
> 
> This patch does not yet tracks async stacks for FileWriter and FileReader.
> 
> BUG=272416, 390863
> R=kinuko@chromium.org, nhiroki@chromium.org, yurys
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178149

TBR=kinuko@chromium.org,nhiroki@chromium.org,yurys@chromium.org,aandrey@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=272416, 390863

Review URL: https://codereview.chromium.org/397843009

git-svn-id: svn://svn.chromium.org/blink/trunk@178269 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix image-rendering: pixelated on HiDPI screens.

An image with layout size equal to the image size should use InterpolationNone
because, on HiDPI screens, it will actually be upscaled.

BUG=391351

Review URL: https://codereview.chromium.org/385053002

git-svn-id: svn://svn.chromium.org/blink/trunk@178270 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilapn: Prepare moving TimeRange to Oilpan

BUG=340522

Review URL: https://codereview.chromium.org/392743002

git-svn-id: svn://svn.chromium.org/blink/trunk@178271 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: remove more Revealer usages from sdk/

This gets rid of remaining WebInspector.Revealer usage in
DOMModel and in OverridesSupport.js

BUG=

Review URL: https://codereview.chromium.org/394843002

git-svn-id: svn://svn.chromium.org/blink/trunk@178272 bbb929c8-8fbe-4397-9dbb-9b2b20218538