DevTools: introduce editor shortcuts section in shortcuts screen

TL;DR: This patch reorganizes shortcut listing on Shortcuts Screen in
devtools and adds 4 more editor shortcuts.

So far we've used to have a single "Sources panel" section in shortcuts
screen. However, with the addition of 4 new editor-specific shortcuts
into the listing (Ctrl-M, Ctrl-D, Ctrl-U, Ctrl-Space) the list becomes
way too hard to read.
The patch suggests splitting the section into "Debugger" and
"Editor".

R=vsevik, pfeldman

Review URL: https://codereview.chromium.org/390113002

git-svn-id: svn://svn.chromium.org/blink/trunk@178174 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Refactoring: make use of Array.keySet

Review URL: https://codereview.chromium.org/396643002

git-svn-id: svn://svn.chromium.org/blink/trunk@178175 bbb929c8-8fbe-4397-9dbb-9b2b20218538
InspectorResourceAgent::delayedRemoveReplayXHR should ref before deref-ing XHR

delayedRemoveReplayXHR derefs the target XHR before adding its ref.
If the XHR ref count is 1, this may drop reference of the XHR and will ref() the dead XHR.

This CL avoids the issue by swapping its operation order.

TBR=haraken, tyoshino, vsevik
TEST=http/tests/inspector/network/network-xhr-replay.html will not crash
BUG=None

Review URL: https://codereview.chromium.org/397633002

git-svn-id: svn://svn.chromium.org/blink/trunk@178177 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[DevTools] Do not pass corrupted page bounds to embedder.

BUG=393520

Review URL: https://codereview.chromium.org/391093002

git-svn-id: svn://svn.chromium.org/blink/trunk@178178 bbb929c8-8fbe-4397-9dbb-9b2b20218538