Web Inspector: Closed computed style sidebar pane rebuilds, resulting in slowness

Web Inspector: Closed computed style sidebar pane rebuilds, resulting in slowness
https://bugs.webkit.org/show_bug.cgi?id=77865

Reviewed by Pavel Feldman.

Source/WebCore:

Test: inspector/styles/lazy-computed-style.html

* inspector/front-end/StylesSidebarPane.js:
(WebInspector.StylesSidebarPane):
(WebInspector.StylesSidebarPane.prototype._executeRebuildUpdate):
(WebInspector.StylesSidebarPane.prototype._refreshComputedStyleSection):
(WebInspector.ComputedStyleSidebarPane.prototype.expand):
(WebInspector.ComputedStylePropertiesSection.prototype.onpopulate):

LayoutTests:

* http/tests/inspector/elements-test.js:
(initialize_ElementTest.InspectorTest.selectNodeAndWaitForStylesWithComputed.stylesCallback):
(initialize_ElementTest.InspectorTest.selectNodeAndWaitForStylesWithComputed):
* inspector/elements/elements-panel-styles.html:
* inspector/styles/css-live-edit.html:
* inspector/styles/lazy-computed-style-expected.txt: Added.
* inspector/styles/lazy-computed-style.html: Added.
* inspector/styles/styles-computed-trace.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107055 268f45cc-cd09-0410-ab3c-d52691b4dbfc