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

2 files changed, 39 insertions, 13 deletions

diff --git a/chrome/renderer/render_view.cc b/chrome/renderer/render_view.cc
index 8a311af..33a25de 100644
--- a/chrome/renderer/render_view.cc
+++ b/chrome/renderer/render_view.cc
@@ -15,6 +15,7 @@
 #include "app/resource_bundle.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
+#include "base/field_trial.h"
 #include "base/gfx/png_encoder.h"
 #include "base/gfx/native_widget_types.h"
 #include "base/string_piece.h"
@@ -249,7 +250,7 @@ RenderView* RenderView::Create(
 void RenderView::SetNextPageID(int32 next_page_id) {
   // This method should only be called during process startup, and the given
   // page id had better not exceed our current next page id!
-  DCHECK(next_page_id_ == 1);
+  DCHECK_EQ(next_page_id_, 1);
   DCHECK(next_page_id >= next_page_id_);
   next_page_id_ = next_page_id;
 }
@@ -534,7 +535,7 @@ void RenderView::PrintPage(const ViewMsg_PrintPage_Params& params,
 
   // Get the size of the compiled EMF.
   unsigned buf_size = emf.GetDataSize();
-  DCHECK(buf_size > 128);
+  DCHECK_GT(buf_size, 128u);
   ViewHostMsg_DidPrintPage_Params page_params;
   page_params.data_size = 0;
   page_params.emf_data_handle = NULL;
@@ -1532,7 +1533,7 @@ void RenderView::DocumentElementAvailable(WebFrame* frame) {
     frame->GrantUniversalAccess();
 
   // Tell extensions to self-register their js contexts.
-  // TODO:(rafaelw): This is kind of gross. We need a way to call through
+  // TODO(rafaelw): This is kind of gross. We need a way to call through
   // the glue layer to retrieve the current v8::Context.
   if (frame->GetURL().SchemeIs(chrome::kExtensionScheme))
     ExtensionProcessBindings::RegisterExtensionContext(frame);
@@ -3009,19 +3010,33 @@ void RenderView::DumpLoadHistograms() const {
 
   // Client side redirects will have no request time
   if (request_time.ToInternalValue() != 0) {
-    UMA_HISTOGRAM_TIMES("Renderer.All.RequestToStart", request_to_start);
-    UMA_HISTOGRAM_TIMES("Renderer.All.RequestToFinish", request_to_finish);
+    UMA_HISTOGRAM_MEDIUM_TIMES(
+        FieldTrial::MakeName("Renderer2.RequestToStart", "DnsImpact").data(),
+        request_to_start);
+    UMA_HISTOGRAM_MEDIUM_TIMES(
+        FieldTrial::MakeName("Renderer2.RequestToFinish", "DnsImpact").data(),
+        request_to_finish);
     if (request_to_first_layout.ToInternalValue() >= 0) {
-      UMA_HISTOGRAM_TIMES(
-        "Renderer.All.RequestToFirstLayout", request_to_first_layout);
+      UMA_HISTOGRAM_MEDIUM_TIMES(
+          FieldTrial::MakeName("Renderer2.RequestToFirstLayout",
+                               "DnsImpact").data(),
+          request_to_first_layout);
     }
   }
-  UMA_HISTOGRAM_TIMES("Renderer.All.StartToFinishDoc", start_to_finish_doc);
-  UMA_HISTOGRAM_TIMES("Renderer.All.FinishDocToFinish", finish_doc_to_finish);
-  UMA_HISTOGRAM_TIMES("Renderer.All.StartToFinish", start_to_finish);
+  UMA_HISTOGRAM_MEDIUM_TIMES(
+      FieldTrial::MakeName("Renderer2.StartToFinishDoc", "DnsImpact").data(),
+      start_to_finish_doc);
+  UMA_HISTOGRAM_MEDIUM_TIMES(
+      FieldTrial::MakeName("Renderer2.FinishDocToFinish", "DnsImpact").data(),
+      finish_doc_to_finish);
+  UMA_HISTOGRAM_MEDIUM_TIMES(
+      FieldTrial::MakeName("Renderer2.StartToFinish", "DnsImpact").data(),
+      start_to_finish);
   if (start_to_first_layout.ToInternalValue() >= 0) {
-    UMA_HISTOGRAM_TIMES(
-      "Renderer.All.StartToFirstLayout", start_to_first_layout);
+    UMA_HISTOGRAM_MEDIUM_TIMES(
+        FieldTrial::MakeName("Renderer2.StartToFirstLayout",
+                             "DnsImpact").data(),
+        start_to_first_layout);
   }
 }
 
diff --git a/chrome/renderer/renderer_main.cc b/chrome/renderer/renderer_main.cc
index 74b5334..fc4d291 100644
--- a/chrome/renderer/renderer_main.cc
+++ b/chrome/renderer/renderer_main.cc
@@ -5,6 +5,7 @@
 #include "app/l10n_util.h"
 #include "app/resource_bundle.h"
 #include "base/command_line.h"
+#include "base/field_trial.h"
 #include "base/histogram.h"
 #include "base/message_loop.h"
 #include "base/path_service.h"
@@ -88,12 +89,22 @@ int RendererMain(const MainFunctionParams& parameters) {
   platform.InitSandboxTests(no_sandbox);
 
   // Initialize histogram statistics gathering system.
-  // Don't create StatisticsRecorde in the single process mode.
+  // Don't create StatisticsRecorder in the single process mode.
   scoped_ptr<StatisticsRecorder> statistics;
   if (!StatisticsRecorder::WasStarted()) {
     statistics.reset(new StatisticsRecorder());
   }
 
+  // Initialize statistical testing infrastructure.
+  FieldTrialList field_trial;
+  // Ensure any field trials in browser are reflected into renderer.
+  if (parsed_command_line.HasSwitch(switches::kForceFieldTestNameAndValue)) {
+    std::string persistent(WideToASCII(parsed_command_line.GetSwitchValue(
+        switches::kForceFieldTestNameAndValue)));
+    FieldTrial *field_trial = FieldTrial::RestorePersistentString(persistent);
+    DCHECK(field_trial);
+  }
+
   {
     RenderProcess render_process;
     bool run_loop = true;