Add GetURL() and WaitForJSExpression() functions

tools/chrome_proxy/webdriver/common.py

Index: tools/chrome_proxy/webdriver/common.py
diff --git a/tools/chrome_proxy/webdriver/common.py b/tools/chrome_proxy/webdriver/common.py
index d44ceabeae52136d56be5817513bf2804709bd15..c66f4afd941ee59c91a388827402870200f8f2bb 100644
--- a/tools/chrome_proxy/webdriver/common.py
+++ b/tools/chrome_proxy/webdriver/common.py
@@ -219,6 +219,15 @@ class TestDriver:
     self._driver.set_page_load_timeout(timeout)
     self._driver.get(self._url)
 
+  def GetURL(self, url, timeout=30):

[RyanSturm, 2016/12/12 20:02:46]

I'd prefer LoadURL. This seems a little backwards based on the API of selenium.

Read my other comment about removing LoadPage/SetURL.

[Robert Ogden, 2016/12/13 16:36:31]

Done.

+    """Convenience function for SetURL() followed by LoadPage()
+      Args:
+        url: the URL to navigate to
+        timeout: the time in seconds to load the page before timing out
+    """
+    self.SetURL(url)

[RyanSturm, 2016/12/12 20:02:46]

For now, forcing us to use GetURL with a param everytime might be best.

I don't think there is a strong need to introduce a convenience function, so
maybe just keep it to one method.

Let me know if there are other uses for self._url that I am not thinking of, but
it seems unneccesary since the test will manage what urls it is navigating to.

This use case is sort of ambiguously defined:
SetURL("a")
LoadPage() 
GetURL("b")
LoadPage()

I think I'd prefer the final LoadPage() to load the page from SetURL (i.e. "a"),
but if we are forced to only use GetURL, it would have to look like:
GetURL("a")
GetURL("b")
GetURL("a"/"b") (depending on what the consumer wanted)

[Robert Ogden, 2016/12/13 16:36:31]

Acknowledged.

+    self.LoadPage(timeout)
+
   def ExecuteJavascript(self, script, timeout=30):
     """Executes the given javascript in the browser's current page in an
     anonymous function.
@@ -260,6 +269,29 @@ class TestDriver:
     string_response = self.ExecuteJavascriptStatement(js_query)
     return json.loads(string_response)
 
+  def WaitForJavascriptExpression(self, expression, timeout, min_poll=0.1,
+      max_poll=1):
+    """Waits for the given Javascript expression to evaluate to True within the
+    given timeout. This method polls the Javascript expression within the range
+    of min_poll and max_poll.
+
+    Args:
+      expression: The Javascript expression to poll, as a string
+      min_poll: The most frequently to poll as a float
+      max_poll: The least frequently to poll as a float
+    Returns: the result of the expression
+    """
+    poll_interval = max(min(max_poll, float(timeout) / 10.0), min_poll)
+    result = self.ExecuteJavascriptStatement(expression)
+    total_waited_time = 0
+    while not result and total_waited_time < timeout:
+      time.sleep(poll_interval)
+      total_waited_time += poll_interval
+      result = self.ExecuteJavascriptStatement(expression)
+    if not result:
+      raise Exception('%s not true after %f seconds' % (expression, timeout))
+    return result
+
   def GetPerformanceLogs(self, method_filter=r'Network\.responseReceived'):
     """Returns all logged Performance events from Chrome.