[bfcache] Do not mark trial as active for low-memory devices.

At the moment we are accidentally marking kBackForwardCache feature and
associated trial as active even when it is disabled by low-memory
config. Add a test to ensure that it does not regress in the future.

R=arthursonzogni@chromium.org,sreejakshetty@chromium.org
BUG=1057081

Change-Id: I057ca3a942704eab139c1846dfa87b86e2daedec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2080416Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745451}

content/browser/back_forward_cache_browsertest.cc

@@ -4784,11 +4784,23 @@ class BackForwardCacheBrowserTestForLowMemoryDevices
 // Navigate from A to B and go back.
 IN_PROC_BROWSER_TEST_F(BackForwardCacheBrowserTestForLowMemoryDevices,
                        DisableBFCacheForLowEndDevices) {
-  EXPECT_FALSE(IsBackForwardCacheEnabled());
   ASSERT_TRUE(embedded_test_server()->Start());
   GURL url_a(embedded_test_server()->GetURL("a.com", "/title1.html"));
   GURL url_b(embedded_test_server()->GetURL("b.com", "/title1.html"));
 
+  // Ensure that the trial starts inactive.
+  EXPECT_FALSE(base::FieldTrialList::IsTrialActive(
+      base::FeatureList::GetFieldTrial(features::kBackForwardCache)
+          ->trial_name()));
+
+  EXPECT_FALSE(IsBackForwardCacheEnabled());
+
+  // Ensure that we do not activate the trial when querying bfcache status,
+  // which is protected by low-memory setting.
+  EXPECT_FALSE(base::FieldTrialList::IsTrialActive(
+      base::FeatureList::GetFieldTrial(features::kBackForwardCache)
+          ->trial_name()));
+
   // 1) Navigate to A.
   EXPECT_TRUE(NavigateToURL(shell(), url_a));
   RenderFrameHostImpl* rfh_a = current_frame_host();
@@ -4804,6 +4816,11 @@ IN_PROC_BROWSER_TEST_F(BackForwardCacheBrowserTestForLowMemoryDevices,
   // Nothing is recorded when the memory is less than the threshold value.
   ExpectOutcomeDidNotChange(FROM_HERE);
   ExpectNotRestoredDidNotChange(FROM_HERE);
+
+  // Ensure that the trial still hasn't been activated.
+  EXPECT_FALSE(base::FieldTrialList::IsTrialActive(
+      base::FeatureList::GetFieldTrial(features::kBackForwardCache)
+          ->trial_name()));
 }
 
 // Test for functionality of memory controls in back-forward cache for high

content/browser/frame_host/back_forward_cache_impl.cc

@@ -72,12 +72,16 @@ const base::FeatureParam<ChildProcessImportance> kChildProcessImportanceParam{
 #endif
 
 bool IsServiceWorkerSupported() {
+  if (!DeviceHasEnoughMemoryForBackForwardCache())
+    return false;
   static constexpr base::FeatureParam<bool> service_worker_supported(
       &features::kBackForwardCache, "service_worker_supported", false);
   return service_worker_supported.Get();
 }
 
 bool IsGeolocationSupported() {
+  if (!DeviceHasEnoughMemoryForBackForwardCache())
+    return false;
   static constexpr base::FeatureParam<bool> geolocation_supported(
       &features::kBackForwardCache, "geolocation_supported",
 #if defined(OS_ANDROID)
@@ -95,6 +99,8 @@ bool IsGeolocationSupported() {
 // calls and force all pages to be cached. Should be used only for local testing
 // and debugging -- things will break when this param is used.
 bool ShouldIgnoreBlocklists() {
+  if (!DeviceHasEnoughMemoryForBackForwardCache())
+    return false;
   static constexpr base::FeatureParam<bool> should_ignore_blocklists(
       &features::kBackForwardCache, "should_ignore_blocklists", false);
   return should_ignore_blocklists.Get();