DevTools: [Console] do not add messages until main target resourceTreeModel is loaded

The patch fixes the flakiness in console tests. The core issue was the
linkifying behavior.

The anchor element is created only once when the console message is rendered at the
first time. This happens at a tricky moment of time, because ConsoleView uses
throttler to render its messages, and console layout tests create console
message elements (thus forcing anchor element to be created) independently
during test execution.

There's also a point of time, when the front-end has not yet received
any scriptParsed events, and the inspectedPageURL is not set yet. If we try
to linkify a console message at this moment, we will end up with a "fallback"
anchor, which has an absolute path as its text (a URL without scheme). This
is the thing that happened in tests and resulted in flakiness.

The patch avoids adding console messages in console view until the main target
resourcetreemodel has loaded its resources.

However, these changes pull off the veil from races in the inspector console
tests.

Method InspectorTest.expandConsoleMessages could actually fail expanding
messages. E.g. formatting console message as node does not produce any
element to expand, instead it initiates a round-trip to push node to
front-end, and after that renders the DOM.

The only reason why this was still working is ConsoleView "warming
up" its console view messages.

There are couple of things happenning here in console layout tests:
* InspectorTest.expandConsoleMessages is not allowed to be executed
without a callback. All its clients which do so are updated.
* InspectorTest.expandConsoleMessages now warms up console messages
on its own.
* InspectorTest.expandConsoleTreeElements method was used from a single
test, and was removed so that the "warming up" functionality is not
duplicated. This resulted in some more output in test expectations,
but it still looks legit.

BUG=406283

Review URL: https://codereview.chromium.org/510983003

git-svn-id: svn://svn.chromium.org/blink/trunk@181198 bbb929c8-8fbe-4397-9dbb-9b2b20218538