fix(tooltip): prevent 1px shift in Webkit/Blink

- Only update tooltip position when content changes, instead of every $digest

Fixes #3964

Author: cvn

src/tooltip/test/tooltip.spec.js

@@ -474,24 +474,26 @@ describe( 'tooltip positioning', function() {
     tooltipScope = elmScope.$$childTail;
   }));
 
-  it( 'should re-position on every digest', inject( function ($timeout) {
+  it( 'should re-position when value changes', inject( function ($timeout) {
     elm.trigger( 'mouseenter' );
 
     scope.$digest();
     $timeout.flush();
     var startingPositionCalls = $position.positionElements.calls.count();
 
+    scope.text = 'New Text';
     scope.$digest();
     $timeout.flush();
+    expect(elm.attr('tooltip')).toBe( 'New Text' );
     expect($position.positionElements.calls.count()).toEqual(startingPositionCalls + 1);
     // Check that positionElements was called with elm
     expect($position.positionElements.calls.argsFor(startingPositionCalls)[0][0])
       .toBe(elm[0]);
 
     scope.$digest();
-    $timeout.flush();
-    expect($position.positionElements.calls.count()).toEqual(startingPositionCalls + 2);
-    expect($position.positionElements.calls.argsFor(startingPositionCalls + 1)[0][0])
+    $timeout.verifyNoPendingTasks();
+    expect($position.positionElements.calls.count()).toEqual(startingPositionCalls + 1);
+    expect($position.positionElements.calls.argsFor(startingPositionCalls)[0][0])
       .toBe(elm[0]);
     scope.$digest();
   }));

src/tooltip/tooltip.js

@@ -136,6 +136,10 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
               tooltip.css( ttPosition );
             };
 
+            var positionTooltipAsync = function () {
+              $timeout(positionTooltip, 0, false);
+            };
+
             // Set up the correct scope to allow transclusion later
             ttScope.origScope = scope;
 
@@ -246,12 +250,9 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
                 }
               });
 
-              tooltipLinkedScope.$watch(function () {
-                $timeout(positionTooltip, 0, false);
-              });
-
               if (options.useContentExp) {
                 tooltipLinkedScope.$watch('contentExp()', function (val) {
+                  positionTooltipAsync();
                   if (!val && ttScope.isOpen ) {
                     hide();
                   }
@@ -287,6 +288,7 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
             if (!options.useContentExp) {
               attrs.$observe( type, function ( val ) {
                 ttScope.content = val;
+                positionTooltipAsync();
 
                 if (!val && ttScope.isOpen ) {
                   hide();
@@ -302,6 +304,7 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
 
             attrs.$observe( prefix+'Title', function ( val ) {
               ttScope.title = val;
+              positionTooltipAsync();
             });
 
             function prepPopupClass() {