Devtools UI: Remove redundant tooltips

Source/devtools/front_end/ui/treeoutline.js

Index: Source/devtools/front_end/ui/treeoutline.js
diff --git a/Source/devtools/front_end/ui/treeoutline.js b/Source/devtools/front_end/ui/treeoutline.js
index 08950c6777168b68734c2ba076fd474ef0a0834f..b1284f884e1f5bed5bd185920cb6df4cfb2b6687 100644
--- a/Source/devtools/front_end/ui/treeoutline.js
+++ b/Source/devtools/front_end/ui/treeoutline.js
@@ -312,8 +312,6 @@ function TreeElement(title, expandable)
     this._listItemNode.treeElement = this;
     if (title)
         this.title = title;
-    if (typeof title === "string")
-        this.tooltip = title;

[paulirish, 2015/08/03 16:26:20]

Appears to be useful for truncated strings like data uris

http://i.imgur.com/aOd4vGd.png

I'd be fine with removing if we knew the displayed text was identical, but
otherwise it seems useful to keep for these cases

[samli, 2015/08/05 07:53:31]

This is not that and still works. The only instances I could find where this was
used was where the string was either empty or:
CPU PROFILES
HEAP SNAPSHOTS
HEAP TIMELINES
RESULTS

This is actually where the empty tooltip bug is coming from.

     this._listItemNode.addEventListener("mousedown", this._handleMouseDown.bind(this), false);
     this._listItemNode.addEventListener("selectstart", this._treeElementSelectStart.bind(this), false);
     this._listItemNode.addEventListener("click", this._treeElementToggled.bind(this), false);