Facilitate a FieldTrial in the renderer

I added a command line for the renderer that accepts a FieldTrial
name and value, and forces that value to be activated in the
renderer.  As a result, any FieldTrial setting that is specified
by the browser process can be set (forced) in the renderer
process.  Such settings can then be used to establish names
of histograms, which means all processes can work in sync
on a single field trial (and generate data).  This should
allow A/B tests to be run that modulate the page load times.

Dave: Please review/confirm that you are happy with the changes to
render_view.cc.  Note that all I did was change the names and limits
for the histograms (they now go up to 3 minutes).  The MakeName()
allows me to get an A/B test of the impact of DNS pre-resolution.

Mike: Please review the code for passing along switch settings.

r=davemoore,mbelshe
Review URL: http://codereview.chromium.org/115525

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@16460 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 12 insertions, 0 deletions

diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index f7e495b..e93abe7 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -454,6 +454,18 @@ const wchar_t kDisableAudio[]                  = L"disable-audio";
 // is cleaned up and playback testing completed.
 const wchar_t kSimpleDataSource[]              = L"simple-data-source";
 
+// Some field tests may be performed in the browser, and the randomly selected
+// outcome needs to be propogated to the renderer to appropriately modify the
+// histogram names that will be tested.  This command line argument is only
+// parsed by the renderer, and consists of a field test name, and a forced
+// selection of an outcome.  For example, if a field test "DnsImpact" has
+// selected "_disabled_prefetch" as a current test, then the render should be
+// passed the command line:
+//      force-fieldtest=DnsImpact/_disabled_prefetch
+// The renderer will then force said named field test to exist, and will force
+// the selected outcome to have the indicated text value.
+const wchar_t kForceFieldTestNameAndValue[]    = L"force-fieldtest";
+
 // Enables the prototype of the next version of the New Tab page.
 const wchar_t kNewNewTabPage[]                 = L"new-new-tab-page";