DevTools: Add inertia to flamechart dragging.

third_party/WebKit/Source/devtools/front_end/ui/UIUtils.js

Index: third_party/WebKit/Source/devtools/front_end/ui/UIUtils.js
diff --git a/third_party/WebKit/Source/devtools/front_end/ui/UIUtils.js b/third_party/WebKit/Source/devtools/front_end/ui/UIUtils.js
index cbe69e3c758bfc10100bda4ce8c597f1c6107c45..127399500c182557787381c0b1dd1b56984091d9 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui/UIUtils.js
+++ b/third_party/WebKit/Source/devtools/front_end/ui/UIUtils.js
@@ -197,6 +197,81 @@ WebInspector._elementDragEnd = function(event)
 }
 
 /**
+ * @param {!Element} element
+ * @param {function(number, number, !MouseEvent): boolean} elementDragStart
+ * @param {function(number, number)} elementDrag
+ * @param {function(number, number)} elementDragEnd
+ * @param {string} cursor
+ * @param {?string=} hoverCursor
+ * @param {number=} startDelay
+ * @param {number=} friction
+ */
+WebInspector.installInertialDragHandle = function(element, elementDragStart, elementDrag, elementDragEnd, cursor, hoverCursor, startDelay, friction)
+{
+    WebInspector.installDragHandle(element, drag.bind(null, elementDragStart), drag.bind(null, elementDrag), dragEnd, cursor, hoverCursor, startDelay);
+    if (typeof friction !== "number")
+        friction = 50;
+    var lastX;
+    var lastY;
+    var lastTime;
+    var velocityX;
+    var velocityY;
+    var holding = false;
+
+    /**
+     * @param {function(number, number, !MouseEvent): boolean} callback
+     * @param {!MouseEvent} event
+     * @return {boolean}
+     */
+    function drag(callback, event)
+    {
+        lastTime = window.performance.now();
+        lastX = event.pageX;
+        lastY = event.pageY;
+        holding = true;
+        return callback(lastX, lastY, event);
+    }
+
+    /**
+     * @param {!MouseEvent} event
+     */
+    function dragEnd(event)
+    {
+        var now = window.performance.now();
+        var duration = now - lastTime || 1;
+        const maxVelocity = 4; // 4px per millisecond.
+        velocityX = Number.constrain((event.pageX - lastX) / duration, -maxVelocity, maxVelocity);
+        velocityY = Number.constrain((event.pageY - lastY) / duration, -maxVelocity, maxVelocity);
+        lastX = event.pageX;
+        lastY = event.pageY;
+        lastTime = now;
+        holding = false;
+        animationStep();
+    }
+
+    function animationStep()
+    {
+        var v2 = velocityX * velocityX + velocityY * velocityY;
+        if (v2 < 0.001 || holding) {
+            elementDragEnd(lastX, lastY);
+            return;
+        }
+        element.window().requestAnimationFrame(animationStep);
+        var now = window.performance.now();
+        var duration = now - lastTime;
+        if (!duration)
+            return;
+        lastTime = now;
+        lastX += velocityX * duration;
+        lastY += velocityY * duration;
+        var k = Math.pow(1 / (1 + friction), duration / 1000);
+        velocityX *= k;
+        velocityY *= k;
+        elementDrag(lastX, lastY);
+    }
+}
+
+/**
  * @constructor
  * @param {!Document} document
  * @param {boolean=} dimmed