predictors: Also track "no-cache" and "must-revalidate" resources.

chrome/browser/predictors/resource_prefetch_predictor.cc

Index: chrome/browser/predictors/resource_prefetch_predictor.cc
diff --git a/chrome/browser/predictors/resource_prefetch_predictor.cc b/chrome/browser/predictors/resource_prefetch_predictor.cc
index 497a359675382ad9b1b6580fae3483bbed7f5ca5..7d2abe6442acd2875f18ad9067e1578d6ecd8d91 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.cc
+++ b/chrome/browser/predictors/resource_prefetch_predictor.cc
@@ -63,7 +63,7 @@ enum ResourceStatus {
   RESOURCE_STATUS_UNSUPPORTED_RESOURCE_TYPE = 4,
   RESOURCE_STATUS_NOT_GET = 8,
   RESOURCE_STATUS_URL_TOO_LONG = 16,
-  RESOURCE_STATUS_NOT_CACHEABLE = 32,
+  RESOURCE_STATUS_NO_STORE = 32,

[pasko, 2016/08/09 09:31:11]

this enum is used in a histogram, hence it should not be updated, fields can
only be added, otherwise it is not possible to make a histograms.xml that serves
all datapoints.

I found that this histogram has data collected on 2015-06-09.

[Benoit L, 2016/08/09 12:24:38]

Acknowledged.

   RESOURCE_STATUS_HEADERS_MISSING = 64,
   RESOURCE_STATUS_MAX = 128,
 };
@@ -280,8 +280,8 @@ bool ResourcePrefetchPredictor::IsHandledSubresource(
   if (!response->response_info().headers.get())
     resource_status |= RESOURCE_STATUS_HEADERS_MISSING;
 
-  if (!IsCacheable(response))
-    resource_status |= RESOURCE_STATUS_NOT_CACHEABLE;
+  if (IsNoStore(response))
+    resource_status |= RESOURCE_STATUS_NO_STORE;
 
   UMA_HISTOGRAM_ENUMERATION("ResourcePrefetchPredictor.ResourceStatus",

[pasko, 2016/08/09 09:31:11]

do we actually need all of this histogram? Alternatively we could record counts
for each resource status. We could have interesting combinations as well, like
3, 7, 35, 36 and 39. They would be more readable this way on the dashboard. 

[Benoit L, 2016/08/09 12:24:38]

Per offline discussion, removed the histogram (but kept the enum for now, used
for debugging).
Done.

                             resource_status,
@@ -312,20 +312,14 @@ bool ResourcePrefetchPredictor::IsHandledResourceType(
 }
 
 // static
-bool ResourcePrefetchPredictor::IsCacheable(const net::URLRequest* response) {
+bool ResourcePrefetchPredictor::IsNoStore(const net::URLRequest* response) {
   if (response->was_cached())
-    return true;
+    return false;
 
-  // For non cached responses, we will ensure that the freshness lifetime is
-  // some sane value.
   const net::HttpResponseInfo& response_info = response->response_info();
   if (!response_info.headers.get())
     return false;
-  base::Time response_time(response_info.response_time);
-  response_time += base::TimeDelta::FromSeconds(1);
-  base::TimeDelta freshness =
-      response_info.headers->GetFreshnessLifetimes(response_time).freshness;
-  return freshness > base::TimeDelta();
+  return response_info.headers->HasHeaderValue("cache-control", "no-store");
 }
 
 // static