[Telemetry] Fix --cold-load-percent.

Previously, we didn't properly clear all the network caches.
1. DNS and predictor caches were left in tact. This was fixed by calling the
   net benchmarking extension methods.
2. Live resources in the memory cache were left in tact. This is fixed by
   navigating to about:blank to destroy the old renderer.

Also, --enable-net-benchmarking is supported on the stable channel, so we can
remove the workaround.

With this, cold loads are consistent on Android:

*RESULT cold_times: page_load_time= [4637,4493,4479,4564,4611,4549] ms
Avg cold_times: 4555.500000ms
Sd  cold_times: 62.602716ms
RESULT warm_times_by_url: http___www.youtube.com_watch?v_LIJOhk6FscY= [2122,2104,2079,2094] ms
Avg warm_times_by_url: 2099.750000ms
Sd  warm_times_by_url: 18.043928ms

BUG=

Review URL: https://codereview.chromium.org/165193002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251252 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/measurements/page_cycler.py

@@ -80,7 +80,7 @@ class PageCycler(page_measurement.PageMeasurement):
   def WillNavigateToPage(self, page, tab):
     page.script_to_evaluate_on_commit = self._page_cycler_js
     if self.ShouldRunCold(page.url):
-      tab.ClearCache()
+      tab.ClearCache(force=True)
     if self._report_speed_index:
       self._speedindex_metric.Start(page, tab)
 

tools/perf/measurements/page_cycler_unittest.py

@@ -38,7 +38,8 @@ class FakePage(object):
 class FakeTab(object):
   def __init__(self):
     self.clear_cache_calls = 0
-  def ClearCache(self):
+  def ClearCache(self, force=False):
+    assert force
     self.clear_cache_calls += 1
   def EvaluateJavaScript(self, _):
     return 1

tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py

@@ -93,9 +93,10 @@ class ChromeBrowserBackend(browser_backend.BrowserBackend):
     args = []
     args.extend(self.browser_options.extra_browser_args)
     args.append('--disable-background-networking')
+    args.append('--enable-net-benchmarking')
     args.append('--metrics-recording-only')
-    args.append('--no-first-run')
     args.append('--no-default-browser-check')
+    args.append('--no-first-run')
     args.append('--no-proxy-server')
     if self.browser_options.netsim:
       args.append('--ignore-certificate-errors')

tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py

@@ -55,7 +55,6 @@ class DesktopBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
     self._browser_directory = browser_directory
     self._port = None
     self._profile_dir = None
-    self._supports_net_benchmarking = True
     self._tmp_minidump_dir = tempfile.mkdtemp()
 
     self._SetupProfile()
@@ -119,10 +118,6 @@ class DesktopBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
       args.append('--window-size=1280,1024')
       if self._flash_path:
         args.append('--ppapi-flash-path=%s' % self._flash_path)
-      if self._supports_net_benchmarking:
-        args.append('--enable-net-benchmarking')
-      else:
-        args.append('--enable-benchmarking')
       if not self.browser_options.dont_override_profile:
         args.append('--user-data-dir=%s' % self._tmp_profile_dir)
     return args
@@ -140,13 +135,6 @@ class DesktopBrowserBackend(chrome_browser_backend.ChromeBrowserBackend):
   def Start(self):
     self._LaunchBrowser()
 
-    # For old chrome versions, might have to relaunch to have the
-    # correct net_benchmarking switch.
-    if self.chrome_branch_number < 1418:
-      self.Close()
-      self._supports_net_benchmarking = False
-      self._LaunchBrowser()
-
   @property
   def pid(self):
     if self._proc:

tools/telemetry/telemetry/core/tab.py

@@ -253,6 +253,21 @@ class Tab(web_contents.WebContents):
   def CollectGarbage(self):
     self._inspector_backend.CollectGarbage()
 
-  def ClearCache(self):
-    """Clears the browser's HTTP disk cache and the tab's HTTP memory cache."""
-    self._inspector_backend.ClearCache()
+  def ClearCache(self, force):
+    """Clears the browser's networking related disk, memory and other caches.
+
+    Args:
+      force: Iff true, navigates to about:blank which destroys the previous
+          renderer, ensuring that even "live" resources in the memory cache are
+          cleared.
+    """
+    self.ExecuteJavaScript("""
+        if (window.chrome && chrome.benchmarking &&
+            chrome.benchmarking.clearCache) {
+          chrome.benchmarking.clearCache();
+          chrome.benchmarking.clearPredictorCache();
+          chrome.benchmarking.clearHostResolverCache();
+        }
+    """)
+    if force:
+      self.Navigate('about:blank')

tools/telemetry/telemetry/page/page_runner.py

@@ -154,7 +154,7 @@ class PageState(object):
 
     if test:
       if test.clear_cache_before_each_run:
-        self.tab.ClearCache()
+        self.tab.ClearCache(force=True)
 
   def ImplicitPageNavigation(self, test=None):
     """Executes the implicit navigation that occurs for every page iteration.

tools/telemetry/telemetry/page/record_wpr.py

@@ -46,7 +46,7 @@ class RecordPage(page_test.PageTest):
 
   def WillNavigateToPage(self, page, tab):
     """Override to ensure all resources are fetched from network."""
-    tab.ClearCache()
+    tab.ClearCache(force=False)
     if self.test:
       self.test.WillNavigateToPage(page, tab)