Add ScrollPageToElement to action_runner.

telemetry/telemetry/internal/actions/scroll_to_element.py

Index: telemetry/telemetry/internal/actions/scroll_to_element.py
diff --git a/telemetry/telemetry/internal/actions/scroll_to_element.py b/telemetry/telemetry/internal/actions/scroll_to_element.py
new file mode 100644
index 0000000000000000000000000000000000000000..8f6302d1b967d854a2ffdfc9107c3a7e3df7d7b3
--- /dev/null
+++ b/telemetry/telemetry/internal/actions/scroll_to_element.py
@@ -0,0 +1,65 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+from telemetry.internal.actions import page_action
+from telemetry.internal.actions.scroll import ScrollAction
+
+
+class ScrollToElementAction(page_action.PageAction):
+
+
+  def __init__(self, selector=None, element_function=None,
+               speed_in_pixels_per_second=800):
+    """
+    Args:
+      selector: Css selector to find element with.
+      element_function: js string that evaluates to an element.
+      speed_in_pixels_per_second: Speed in pixels per second to scroll.
+    """
+    super(ScrollToElementAction, self).__init__()
+    self._selector = selector
+    self._element_function = element_function
+    self._speed = speed_in_pixels_per_second
+    self._distance = None
+    self._direction = None
+    self._scroller = None
+    assert (self._selector or self._element_function), (
+        'Must have either selector or element function')
+
+  def WillRunAction(self, tab):
+    if self._selector:
+      element = 'document.querySelector("%s")' % self._selector
+    else:
+      element = self._element_function
+
+    get_distance_js = '''
+      (function(elem){
+        var rect = elem.getBoundingClientRect();
+        if (rect.bottom < 0) {
+          // The bottom of the element is above the viewport.
+          // Scroll up until the top of the element is on screen.
+          return rect.top - (window.innerHeight / 2);
+        }
+        if (rect.top - window.innerHeight >= 0) {
+          // rect.top provides the pixel offset of the element from the
+          // top of the page. Because that exceeds the viewport's height,
+          // we know that the element is below the viewport.
+          return rect.top - (window.innerHeight / 2);
+        }
+        return 0;
+      })(%s);
+    ''' % element
+
+    self._distance = tab.EvaluateJavaScript(get_distance_js)
+    self._direction = 'down' if self._distance > 0 else 'up'
+    self._distance = abs(self._distance)
+    self._scroller = ScrollAction(direction=self._direction,
+                                  distance=self._distance,
+                                  speed_in_pixels_per_second=self._speed)
+
+  def RunAction(self, tab):
+    if self._distance == 0:  # Element is already in view.
+      return
+    self._scroller.WillRunAction(tab)
+    self._scroller.RunAction(tab)