[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

7 files changed, 25 insertions, 20 deletions

diff --git a/tools/perf/measurements/page_cycler.py b/tools/perf/measurements/page_cycler.py
index c02a30b..3c783dd 100644
--- a/tools/perf/measurements/page_cycler.py
+++ b/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)
 
diff --git a/tools/perf/measurements/page_cycler_unittest.py b/tools/perf/measurements/page_cycler_unittest.py
index 13f4cd2..ce0ad12 100644
--- a/tools/perf/measurements/page_cycler_unittest.py
+++ b/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
diff --git a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py b/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
index d1c12a3..43793d7 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/chrome_browser_backend.py
+++ b/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')
diff --git a/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py b/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py
index 904cd92..18a56a4 100644
--- a/tools/telemetry/telemetry/core/backends/chrome/desktop_browser_backend.py
+++ b/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:
diff --git a/tools/telemetry/telemetry/core/tab.py b/tools/telemetry/telemetry/core/tab.py
index d44fc09..8b677df 100644
--- a/tools/telemetry/telemetry/core/tab.py
+++ b/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')
diff --git a/tools/telemetry/telemetry/page/page_runner.py b/tools/telemetry/telemetry/page/page_runner.py
index c209a5d..f52030a 100644
--- a/tools/telemetry/telemetry/page/page_runner.py
+++ b/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.
diff --git a/tools/telemetry/telemetry/page/record_wpr.py b/tools/telemetry/telemetry/page/record_wpr.py
index 9280f2c..6aaec35 100755
--- a/tools/telemetry/telemetry/page/record_wpr.py
+++ b/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)