BackForwardCache: Reland: Allow WebFilesystem with a flag

This CL is reland of http://crrev.com/c/2531155 with some test fixes.

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
Bug: 1151235
Change-Id: I3b3526f180c19d33d6ca16a88efe400fe9bd2c5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2557160Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830876}

content/browser/back_forward_cache_browsertest.cc

@@ -8556,4 +8556,38 @@ IN_PROC_BROWSER_TEST_F(BackForwardCacheBrowserTest, SandboxedFramesNotCached) {
       FROM_HERE);
 }
 
+class BackForwardCacheBrowserTestWithFileSystemAPISupported
+    : public BackForwardCacheBrowserTest {
+ protected:
+  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());
+  GURL url_a(embedded_test_server()->GetURL("/fileapi/request_test.html"));
+  GURL url_b(embedded_test_server()->GetURL("b.com", "/title1.html"));
+
+  // 1) Navigate to a page with WebFileSystem usage.
+  EXPECT_TRUE(NavigateToURL(shell(), url_a));
+  RenderFrameHostImpl* rfh_a = current_frame_host();
+  RenderFrameDeletedObserver deleted(rfh_a);
+
+  // 2) Navigate away.
+  EXPECT_TRUE(NavigateToURL(shell(), url_b));
+  EXPECT_FALSE(deleted.deleted());
+  EXPECT_TRUE(rfh_a->IsInBackForwardCache());
+
+  // 3) Go back to the page with WebFileSystem.
+  web_contents()->GetController().GoBack();
+  EXPECT_TRUE(WaitForLoadStop(shell()->web_contents()));
+  EXPECT_EQ(rfh_a, current_frame_host());
+  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();