DevTools: prettify layout on Shortcuts help screen

BUG=394823

Review URL: https://codereview.chromium.org/400783002

git-svn-id: svn://svn.chromium.org/blink/trunk@178429 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: get rid of obsolete "Sources Panel" section in shortcuts screen

Sources Panel triggered creation of "Sources Panel" section in shortcuts
panel. The variable haven't being used anywhere in the code, and we don't
have a "Sources Panel" any more, thus its safe to remove it.

R=vsevik

Review URL: https://codereview.chromium.org/405583002

git-svn-id: svn://svn.chromium.org/blink/trunk@178430 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Make sure that vtables for garbage collected mixin objects have
vtable entries for the trace method.

If we get garbage collection during construction of an object with
a virtual trace method we need to make sure that all vtables in
the inheritance hierarchy have entries for the trace method.
Otherwise, we can get out-of-bounds access of a super class vtable.

R=erik.corry@gmail.com, haraken@chromium.org, wibling@chromium.org
BUG=382557

Review URL: https://codereview.chromium.org/406523002

git-svn-id: svn://svn.chromium.org/blink/trunk@178431 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Propagate nested importScripts() error events outwards.

If importScripts() evaluation fails, we report the exception wrt the
URL and location of the failing script. Extend that to handle the
nested case, propagating any inner importScripts-induced error event
outwards rather than construct a new one wrt the outer script URL.

R=haraken@chromium.org
BUG=394615

Review URL: https://codereview.chromium.org/404513002

git-svn-id: svn://svn.chromium.org/blink/trunk@178432 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Resolve screen.orientation.lock() promise with undefined.

This is following the current state of the specification.

BUG=162827

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178406

Review URL: https://codereview.chromium.org/400703003

git-svn-id: svn://svn.chromium.org/blink/trunk@178433 bbb929c8-8fbe-4397-9dbb-9b2b20218538