V8LazyEventListener::prepareListenerObject should have a check for a null context

It looks possible that V8LazyEventListener::prepareListenerObject is called with a null ExecutionContext. (I don't know a concrete scenario but it will happen if a parent document requests an event handler of an object in a child document that is already disposed.)

Just like V8LazyEventListener::prepareListenerObject has a check for a null v8::Context, we should have a check for a null ExecutionContext.

BUG=418340
TEST=None. I manually verified that this CL fixes the bug 418340 but failed in minimizing the test case. Cluster Fuzz didn't provide a minimized test.

Review URL: https://codereview.chromium.org/622483002

git-svn-id: svn://svn.chromium.org/blink/trunk@183046 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: fix flakiness of some inspector/elements/styles tests

The flakiness was implied by interference of throttled process applyStyleText
and committing of a new style rule. Helper method relied on
InspectorTest.runAfterPendingDispatches method, which in this case turned
out to be invalid.

BUG=416846, 418483
R=pfeldman, apavlov

Review URL: https://codereview.chromium.org/617473002

git-svn-id: svn://svn.chromium.org/blink/trunk@183047 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Remove remaining usage of resourceView.css deleted in r182834

TBR=pfeldman
BUG=419303
NOTRY=true

Review URL: https://codereview.chromium.org/622533002

git-svn-id: svn://svn.chromium.org/blink/trunk@183048 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: skip edit-dom-actions-shadow while I'm figuring out the flake.

TBR=apavlov
NOTRY=true

Review URL: https://codereview.chromium.org/617233002

git-svn-id: svn://svn.chromium.org/blink/trunk@183049 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: fix Timeline tree item border color

After r182835 it became black. This fixes it to be darker than background of corresponding icon.

BUG=None
NOTRY=True

Review URL: https://codereview.chromium.org/621823002

git-svn-id: svn://svn.chromium.org/blink/trunk@183050 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[CSS Grid Layout] Fix positioned grid items crash

Modify RenderGrid::layoutGridItems() to take care of the positioned
items, otherwise when the tree is invalidated the list of positioned
objects would be empty and we would reach an assert.

More changes related to the absolute positioned items should be done
later, to adapt the behavior to the spec, but this is just a patch to
avoid the crash at this moment.

BUG=402504
TEST=fast/css-grid-layout/positioned-grid-items-crash.html

Review URL: https://codereview.chromium.org/594153002

git-svn-id: svn://svn.chromium.org/blink/trunk@183051 bbb929c8-8fbe-4397-9dbb-9b2b20218538