Bug 1491249 - Implement URL tooltip. r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D7698

--HG--
extra : moz-landing-system : lando

browser/components/urlbar/UrlbarInput.jsm

@@ -104,6 +104,7 @@ class UrlbarInput {
     this.inputField.addEventListener("blur", this);
     this.inputField.addEventListener("focus", this);
     this.inputField.addEventListener("mousedown", this);
+    this.inputField.addEventListener("mouseover", this);
     this.inputField.addEventListener("overflow", this);
     this.inputField.addEventListener("underflow", this);
     this.inputField.addEventListener("scrollend", this);
@@ -210,6 +211,14 @@ class UrlbarInput {
     });
   }
 
+  _updateUrlTooltip() {
+    if (this.focused || !this._inOverflow) {
+      this.inputField.removeAttribute("title");
+    } else {
+      this.inputField.setAttribute("title", this.value);
+    }
+  }
+
   _getSelectedValueForClipboard() {
     // Grab the actual input field's value, not our value, which could
     // include "moz-action:".
@@ -328,9 +337,15 @@ class UrlbarInput {
   }
 
   _on_focus(event) {
+    this._updateUrlTooltip();
+
     this.formatValue();
   }
 
+  _on_mouseover(event) {
+    this._updateUrlTooltip();
+  }
+
   _on_mousedown(event) {
     if (event.button == 0 &&
         event.detail == 2 &&
@@ -390,7 +405,10 @@ class UrlbarInput {
       return;
     }
     this._inOverflow = false;
+
     this._updateTextOverflow();
+
+    this._updateUrlTooltip();
   }
 
   _on_scrollend(event) {