chromeos: Avoid crash on thaw failure if freezing failed.

Avoid an "Unable to thaw renderers." LOG(FATAL) in
RendererFreezer if freezing the renderers also failed
earlier. This is a workaround for unexplained EBADF and
ENOENT errors seen when writing to cgroups.

BUG=chromium:661310
TEST=manual: log in and chmod freezer.state in
     /sys/fs/cgroup/freezer/chrome_renderers/to_be_frozen
     to 444; suspend and resume and check that chrome
     doesn't abort

Review-Url: https://codereview.chromium.org/2575933002
Cr-Commit-Position: refs/heads/master@{#438625}

chrome/browser/chromeos/power/freezer_cgroup_process_manager.cc

@@ -34,7 +34,9 @@ class FreezerCgroupProcessManager::FileWorker {
   explicit FileWorker(scoped_refptr<base::SequencedTaskRunner> file_thread)
       : ui_thread_(content::BrowserThread::GetTaskRunnerForThread(
             content::BrowserThread::UI)),
-        file_thread_(file_thread) {
+        file_thread_(file_thread),
+        enabled_(false),
+        froze_successfully_(false) {
     DCHECK(ui_thread_->RunsTasksOnCurrentThread());
   }
 
@@ -78,7 +80,8 @@ class FreezerCgroupProcessManager::FileWorker {
       return;
     }
 
-    WriteCommandToFile(kFreezeCommand, to_be_frozen_state_path_);
+    froze_successfully_ =
+        WriteCommandToFile(kFreezeCommand, to_be_frozen_state_path_);
   }
 
   void ThawRenderers(ResultCallback callback) {
@@ -91,6 +94,13 @@ class FreezerCgroupProcessManager::FileWorker {
     }
 
     bool result = WriteCommandToFile(kThawCommand, to_be_frozen_state_path_);
+
+    // TODO(derat): For now, lie and report success if thawing failed but
+    // freezing also failed previously. Remove after weird EBADF and ENOENT
+    // problems tracked at http://crbug.com/661310 are fixed.
+    if (!result && !froze_successfully_)
+      result = true;
+
     ui_thread_->PostTask(FROM_HERE, base::Bind(callback, result));
   }
 
@@ -128,6 +138,10 @@ class FreezerCgroupProcessManager::FileWorker {
 
   bool enabled_;
 
+  // True iff FreezeRenderers() wrote its command successfully the last time it
+  // was called.
+  bool froze_successfully_;
+
   DISALLOW_COPY_AND_ASSIGN(FileWorker);
 };