DevTools: fix logic of determining content root for trace layers

We can't rely on draws_content property of layers we get from
tracing, as it may be true for non-content layers. Let's also
check the owner node. However, since there may be cases where
we lack the owner node info, be prepared to draw the entire
layer tree in case we failed to locate content root.

BUG=

Review URL: https://codereview.chromium.org/687963002

git-svn-id: svn://svn.chromium.org/blink/trunk@184720 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: remove dependencies on TimelineUIUtilsImpl in tracing based Timeline

Removed load test as it tests old timeline implementation. There is tracing-timeline-load.html for the tracing based implementation.

Change in TracingTimelineUIUtils.js is actually a improved version of the code added in https://codereview.chromium.org/391373008 as we want to rewrite the text content only in case of JSFrame records.

BUG=428700

Review URL: https://codereview.chromium.org/692043002

git-svn-id: svn://svn.chromium.org/blink/trunk@184727 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: remove unused code showingFirstSearchResult/showingLastSearchResult

BUG=

Review URL: https://codereview.chromium.org/696673002

git-svn-id: svn://svn.chromium.org/blink/trunk@184731 bbb929c8-8fbe-4397-9dbb-9b2b20218538