Optimize propagation of canvas invalidation rectangles to compositor.

The canvas element was propagating its invalidation region all
the way down to the compositor at every draw call in some cases.
This change batches the propagations to do it only once per script
execution task. There was already a TaskObserver in
RecordingImageBufferSurface. This change refactors it to make
HTMLCanvasElement a task observer instead. The the task observer
notification now flows from HTMLCanavasElement down to the ImageBuffer
and ImageBufferSurface, which is more natural because it follows object
ownership order.

BUG=399290

Review URL: https://codereview.chromium.org/435253002

git-svn-id: svn://svn.chromium.org/blink/trunk@179637 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark fast/transforms/shadows.html as flaky on Snow Leopard

TBR=rjwright@chromium.org
BUG=400978

Review URL: https://codereview.chromium.org/450483002

git-svn-id: svn://svn.chromium.org/blink/trunk@179638 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove DialogElement from ContextFeatures, remove plumbing from scripts.

The HTML <dialog> element is stable, and we don't have or need the ability
anymore to conditionally enable it for certain contexts. Remove the plumbing.

BUG=

Review URL: https://codereview.chromium.org/444563004

git-svn-id: svn://svn.chromium.org/blink/trunk@179639 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[CSS Grid Layout] Test coverage for first-line pseudo-element

According to the spec the ::first-line pseudo-element do not apply to
grid containers.

This was already working as expected but we were missing some tests
checking it.

TEST=fast/css-grid-layout/grid-container-ignore-first-line.html
TEST=fast/css-grid-layout/grid-item-first-line-valid.html

BUG=395788

Review URL: https://codereview.chromium.org/437363002

git-svn-id: svn://svn.chromium.org/blink/trunk@179640 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add ES6 Map and Set to global constructors listing expectations

They will be enabled by V8 in an upcoming roll.

BUG=400507
TBR=arv@chromium.org

Review URL: https://codereview.chromium.org/447833002

git-svn-id: svn://svn.chromium.org/blink/trunk@179641 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Properly handle zero height lines with image shape-outside

When a zero height line is supplied and the image shape extends into the
margin box (only possible when a shape-margin is supplied), then only an
empty interval was being returned. This patch makes it properly return
the interval for the line in question.

BUG=397728

Review URL: https://codereview.chromium.org/434623009

git-svn-id: svn://svn.chromium.org/blink/trunk@179642 bbb929c8-8fbe-4397-9dbb-9b2b20218538