Clean up error handling logic for extension tab muting

chrome/browser/ui/tabs/tab_utils.cc

Index: chrome/browser/ui/tabs/tab_utils.cc
diff --git a/chrome/browser/ui/tabs/tab_utils.cc b/chrome/browser/ui/tabs/tab_utils.cc
index cfe6282b03aeb2d6ad9a80104fae4874f394a759..d320b87c98ea5b349659a4a826e8a56598378ba8 100644
--- a/chrome/browser/ui/tabs/tab_utils.cc
+++ b/chrome/browser/ui/tabs/tab_utils.cc
@@ -21,8 +21,15 @@ struct LastMuteMetadata
     : public content::WebContentsUserData<LastMuteMetadata> {
   std::string cause;  // Extension ID or constant from header file
                       // or empty string
+  base::TimeDelta token_bucket;
+  base::TimeTicks last_attempt;
+
  private:
-  explicit LastMuteMetadata(content::WebContents* contents) {}
+  explicit LastMuteMetadata(content::WebContents* contents) {
+    token_bucket =
+        base::TimeDelta::FromSeconds(chrome::kMuteTokenBucketCapacitySeconds);
+    last_attempt = base::TimeTicks::Now();
+  }
   friend class content::WebContentsUserData<LastMuteMetadata>;
 };
 
@@ -32,6 +39,8 @@ namespace chrome {
 
 const char kMutedToggleCauseUser[] = "user";
 const char kMutedToggleCauseCapture[] = "capture";
+const int kMuteTokenBucketCostSeconds = 15;
+const int kMuteTokenBucketCapacitySeconds = 3 * kMuteTokenBucketCostSeconds;
 
 namespace {
 
@@ -91,6 +100,31 @@ TabRecordingIndicatorAnimation::Create() {
   return animation.Pass();
 }
 
+// Only run when cause should be rate limited (i.e. extensions)
+void UpdateTokenBuckets(content::WebContents* contents) {
+  DCHECK(contents);

[miu, 2015/07/18 00:42:42]

To answer your question: The DCHECK here and at the top of
IsTabAudioMutedRateLimited() aren't strictly needed, but they are documentative.
 It's up to you whether to keep them or not.

[Jared Sohn, 2015/07/18 23:57:24]

I am removing them and replacing with a general comment since the current code
just says it cannot be a null pointer but doesn't say that it has initialized
LastMutedMetadata. 

On 2015/07/18 at 00:42:42, miu wrote:

+
+  base::TimeTicks now = base::TimeTicks::Now();
+  base::TimeDelta elapsed_since_last_attempt =
+      now - LastMuteMetadata::FromWebContents(contents)->last_attempt;
+  LastMuteMetadata::FromWebContents(contents)->last_attempt = now;
+
+  // Add tokens to the bucket, proportional to how much time has elapsed, capped
+  // at the maximum capacity.
+  LastMuteMetadata::FromWebContents(contents)->token_bucket = std::min(
+      base::TimeDelta::FromSeconds(chrome::kMuteTokenBucketCapacitySeconds),
+      LastMuteMetadata::FromWebContents(contents)->token_bucket +
+          elapsed_since_last_attempt);
+}
+
+// Only run when cause should be rate limited (i.e. extensions)
+bool IsTabAudioMutedRateLimited(content::WebContents* contents) {
+  DCHECK(contents);
+
+  return (LastMuteMetadata::FromWebContents(contents)->token_bucket <
+          base::TimeDelta::FromSeconds(kMuteTokenBucketCostSeconds));
+}
+
 }  // namespace
 
 bool ShouldTabShowFavicon(int capacity,
@@ -276,16 +310,34 @@ const std::string& GetTabAudioMutedCause(content::WebContents* contents) {
   return LastMuteMetadata::FromWebContents(contents)->cause;
 }
 
-void SetTabAudioMuted(content::WebContents* contents,
-                      bool mute,
-                      const std::string& cause) {
-  if (!contents || !chrome::CanToggleAudioMute(contents))
-    return;
+TabMutedResult SetTabAudioMuted(content::WebContents* contents,
+                                bool mute,
+                                const std::string& cause) {
+  DCHECK(contents);
+
+  if (!IsTabAudioMutingFeatureEnabled())
+    return TAB_MUTED_RESULT_FAIL_NOT_ENABLED;
+
+  if (!chrome::CanToggleAudioMute(contents))
+    return TAB_MUTED_RESULT_FAIL_TABCAPTURE;
 
   LastMuteMetadata::CreateForWebContents(contents);  // Create if not exists.
+
+  if ((cause != kMutedToggleCauseUser) && (cause != kMutedToggleCauseCapture)) {
+    UpdateTokenBuckets(contents);
+
+    if (IsTabAudioMutedRateLimited(contents))
+      return TAB_MUTED_RESULT_FAIL_RATE_LIMITED;
+
+    LastMuteMetadata::FromWebContents(contents)->token_bucket -=
+        base::TimeDelta::FromSeconds(kMuteTokenBucketCostSeconds);
+  }
+
   LastMuteMetadata::FromWebContents(contents)->cause = cause;
 
   contents->SetAudioMuted(mute);
+
+  return TAB_MUTED_RESULT_SUCCESS;
 }
 
 bool IsTabAudioMuted(content::WebContents* contents) {