Drop DidStartHTTPServer to simplify object interactions.

(Will make it easier to move the memory_cache_http_server ownership
from browser to platform.)

The page_cycler measurement was the only customer. This CL includes
an alternate implementation for that.

BUG=404771

Review URL: https://codereview.chromium.org/543243002

Cr-Commit-Position: refs/heads/master@{#294691}

tools/perf/measurements/page_cycler.py

@@ -45,6 +45,7 @@ class PageCycler(page_test.PageTest):
     self._cpu_metric = None
     self._v8_object_stats_metric = None
     self._has_loaded_page = collections.defaultdict(int)
+    self._initial_renderer_url = None  # to avoid cross-renderer navigation
 
   @classmethod
   def AddCommandLineArgs(cls, parser):
@@ -94,12 +95,15 @@ class PageCycler(page_test.PageTest):
     if self._record_v8_object_stats:
       self._v8_object_stats_metric = v8_object_stats.V8ObjectStatsMetric()
 
-  def DidStartHTTPServer(self, tab):
-    # Avoid paying for a cross-renderer navigation on the first page on legacy
-    # page cyclers which use the filesystem.
-    tab.Navigate(tab.browser.http_server.UrlOf('nonexistent.html'))
-
   def WillNavigateToPage(self, page, tab):
+    if page.is_file:
+      # For legacy page cyclers which use the filesystem, do an initial
+      # navigate to avoid paying for a cross-renderer navigation.
+      initial_url = tab.browser.http_server.UrlOf('nonexistent.html')
+      if self._initial_renderer_url != initial_url:
+        self._initial_renderer_url = initial_url
+        tab.Navigate(self._initial_renderer_url)
+
     page.script_to_evaluate_on_commit = self._page_cycler_js
     if self.ShouldRunCold(page.url):
       tab.ClearCache(force=True)

tools/perf/measurements/page_cycler_unittest.py

@@ -38,17 +38,21 @@ class FakePage(object):
   """Used to mock loading a page."""
   def __init__(self, url):
     self.url = url
+    self.is_file = url.startswith('file://')
 
 
 class FakeTab(object):
   """Used to mock a browser tab."""
   def __init__(self):
     self.clear_cache_calls = 0
+    self.navigated_urls = []
   def ClearCache(self, force=False):
     assert force
     self.clear_cache_calls += 1
   def EvaluateJavaScript(self, _):
     return 1
+  def Navigate(self, url):
+    self.navigated_urls.append(url)
   def WaitForJavaScriptExpression(self, _, __):
     pass
   @property
@@ -73,6 +77,13 @@ class FakeBrowser(object):
   def platform(self):
     return FakePlatform()
 
+  @property
+  def http_server(self):
+    class FakeHttpServer(object):
+      def UrlOf(self, url_path):
+        return 'http://fakeserver:99999/%s' % url_path
+    return FakeHttpServer()
+
 
 class FakePlatform(object):
   def GetOSName(self):
@@ -213,3 +224,16 @@ class PageCyclerUnitTest(unittest.TestCase):
           self.assertEqual(value.units, '%')
 
         cycler.DidNavigateToPage(page, tab)
+
+  def testLegacyPagesAvoidCrossRenderNavigation(self):
+    # For legacy page cyclers with file URLs, verify that WillNavigateToPage
+    # does an initial navigate to avoid paying for a cross-renderer navigation.
+    cycler = self.SetUpCycler([], True)
+    pages = [FakePage('file://fakepage1.com'), FakePage('file://fakepage2.com')]
+    tab = FakeTab()
+
+    self.assertEqual([], tab.navigated_urls)
+    for page in pages * 2:
+      cycler.WillNavigateToPage(page, tab)
+      self.assertEqual(
+          ['http://fakeserver:99999/nonexistent.html'], tab.navigated_urls)

tools/telemetry/telemetry/page/page_runner.py

@@ -152,10 +152,8 @@ class PageState(object):
 
   def PreparePage(self, test=None):
     if self.page.is_file:
-      server_started = self.tab.browser.SetHTTPServerDirectories(
-        self.page.page_set.serving_dirs | set([self.page.serving_dir]))
-      if server_started and test:
-        test.DidStartHTTPServer(self.tab)
+      self.tab.browser.SetHTTPServerDirectories(
+          self.page.page_set.serving_dirs | set([self.page.serving_dir]))
 
     if self.page.credentials:
       if not self.tab.browser.credentials.LoginNeeded(

tools/telemetry/telemetry/page/page_test.py

@@ -222,9 +222,6 @@ class PageTest(command_line.Command):
   def DidRunPageRepeats(self, page):
     """Override to do operations after each page is iterated over."""
 
-  def DidStartHTTPServer(self, tab):
-    """Override to do operations after the HTTP server is started."""
-
   def WillNavigateToPage(self, page, tab):
     """Override to do operations before the page is navigated, notably Telemetry
     will already have performed the following operations on the browser before