BackForwardCache: Allow WebFilesystem with a flag

WebFilesystem doesn't have notions of handlers or connections, then it
should be safe to allow pages with WebFilesystem to be put into the
BFcache. Let's allow WebFilesystem for BFcache in order to improve the
BFcache hit rate.

This is implemented behind a flag and the feature is disabled by
default. This means that this CL doesn't change the behavior by default.
We might enable the feature later.

Bug: 1144133
Change-Id: Idf5d9cfb8a4365ae65743c2becc7a4ef8ec66999
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2531155
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829149}

content/browser/back_forward_cache_browsertest.cc

@@ -8555,4 +8555,32 @@ IN_PROC_BROWSER_TEST_F(BackForwardCacheBrowserTest, SandboxedFramesNotCached) {
       FROM_HERE);
 }
 
+class BackForwardCacheBrowserTestWithFileSystemAPISupported
+    : public BackForwardCacheBrowserTest {
+  void SetUpCommandLine(base::CommandLine* command_line) override {
+    EnableFeatureAndSetParams(features::kBackForwardCache,
+                              "file_system_api_supported", "true");
+    BackForwardCacheBrowserTest::SetUpCommandLine(command_line);
+  }
+};
+
+IN_PROC_BROWSER_TEST_F(BackForwardCacheBrowserTestWithFileSystemAPISupported,
+                       CacheWithFileSystemAPI) {
+  ASSERT_TRUE(embedded_test_server()->Start());
+
+  // 1) Navigate to a page with WebFileSystem usage.
+  GURL url(embedded_test_server()->GetURL("/fileapi/request_test.html"));
+  EXPECT_TRUE(NavigateToURL(shell(), url));
+
+  // 2) Navigate away.
+  EXPECT_TRUE(NavigateToURL(
+      shell(), embedded_test_server()->GetURL("b.com", "/title1.html")));
+
+  // 3) Go back to the page with WebFileSystem.
+  web_contents()->GetController().GoBack();
+  EXPECT_TRUE(WaitForLoadStop(shell()->web_contents()));
+  ExpectOutcome(BackForwardCacheMetrics::HistoryNavigationOutcome::kRestored,
+                FROM_HERE);
+}
+
 }  // namespace content

content/browser/renderer_host/back_forward_cache_impl.cc

@@ -88,6 +88,14 @@ bool IsGeolocationSupported() {
   return geolocation_supported.Get();
 }
 
+bool IsFileSystemSupported() {
+  if (!DeviceHasEnoughMemoryForBackForwardCache())
+    return false;
+  static constexpr base::FeatureParam<bool> file_system_api_supported(
+      &features::kBackForwardCache, "file_system_api_supported", false);
+  return file_system_api_supported.Get();
+}
+
 bool IgnoresOutstandingNetworkRequestForTesting() {
   if (!DeviceHasEnoughMemoryForBackForwardCache())
     return false;
@@ -146,7 +154,6 @@ uint64_t GetDisallowedFeatures(RenderFrameHostImpl* rfh,
       FeatureToBit(WebSchedulerTrackedFeature::kSpeechSynthesis) |
       FeatureToBit(WebSchedulerTrackedFeature::kWakeLock) |
       FeatureToBit(WebSchedulerTrackedFeature::kWebDatabase) |
-      FeatureToBit(WebSchedulerTrackedFeature::kWebFileSystem) |
       FeatureToBit(WebSchedulerTrackedFeature::kWebHID) |
       FeatureToBit(WebSchedulerTrackedFeature::kWebLocks) |
       FeatureToBit(WebSchedulerTrackedFeature::kWebRTC) |
@@ -171,6 +178,10 @@ uint64_t GetDisallowedFeatures(RenderFrameHostImpl* rfh,
         FeatureToBit(WebSchedulerTrackedFeature::kOutstandingNetworkRequestXHR);
   }
 
+  if (!IsFileSystemSupported()) {
+    result |= FeatureToBit(WebSchedulerTrackedFeature::kWebFileSystem);
+  }
+
   if (requested_features == RequestedFeatures::kOnlySticky) {
     // Remove all non-sticky features from |result|.
     result &= blink::scheduler::StickyFeaturesBitmask();