Fix Resource Priorities and Scheduling (Chrome Side)

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 1e4392e3f943535bc79a97015283acdd12ce6494..331a597ea2104070dc72b334e85dad1ee29aca1d 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -1218,13 +1218,48 @@ void MaybeAppendBlinkSettingsSwitchForFieldTrial(
       }
     }
   }
+
+  // Flags for the ResourcePriorities field trial. The settings are
+  // encoded in the field trial group name instead of as variations
+  // because the variations code is not accessible from the loader.
+  //
+  // The group name encoding looks like this:
+  //  <descriptiveName>_ABCDE_E2_F_G
+  //    A - fetchDeferLateScripts (1 for true, 0 for false)
+  //    B - fetchIncreaseFontPriority (1 for true, 0 for false)
+  //    C - fetchIncreaseAsyncScriptPriority (1 for true, 0 for false)
+  //    D - fetchIncreasePriorities (1 for true, 0 for false)
+  //    E - fetchEnableLayoutBlockingThreshold (1 for true, 0 for false)
+  //    E2 - fetchLayoutBlockingThreshold (Numeric)
+  //    F - fetchMaxNumDelayableWhileLayoutBlocking (Numeric)
+  //    G - fetchMaxNumDelayableRequests (Numeric)
+  //
+  // Only A-D are relevant to blink and exposed as settings
+  // Any group names (Control, Default, etc) will not match the pattern or
+  // flags and will get the default settings which is the expected behavior.
+  std::string resource_priorities_trial_group =
+      base::FieldTrialList::FindFullName("ResourcePriorities");
+  std::vector<std::string> split_group(
+      base::SplitString(resource_priorities_trial_group, "_",
+                        base::KEEP_WHITESPACE, base::SPLIT_WANT_ALL));
+  if (split_group.size() == 5 && split_group[1].length() == 5) {
+    if (split_group[1].at(0) == '1')
+      blink_settings.push_back("fetchDeferLateScripts=true");
+    if (split_group[1].at(1) == '1')
+      blink_settings.push_back("fetchIncreaseFontPriority=true");
+    if (split_group[1].at(2) == '1')
+      blink_settings.push_back("fetchIncreaseAsyncScriptPriority=true");
+    if (split_group[1].at(3) == '1')
+      blink_settings.push_back("fetchIncreasePriorities=true");

[mmenke, 2015/08/11 17:57:23]

Is the code to implement these landed yet?

[Pat Meenan, 2015/08/12 16:20:59]

Not yet.  Currently under review: https://codereview.chromium.org/1246493002/

I'll address all of the other issues and let you know when the blink side has
landed in case the names change.

+  }
+
   if (blink_settings.empty()) {
     return;
   }
 
   if (browser_command_line.HasSwitch(switches::kBlinkSettings) ||
       command_line->HasSwitch(switches::kBlinkSettings)) {
-    // The field trial is configured to force users that specify the
+    // The field trials should be configured to force users that specify the
     // blink-settings flag into a group with no params, and we return
     // above if no params were specified, so it's an error if we reach
     // this point.