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..96c8f7533dac54ea288dd71f73416af730ff830f 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>;
 };
 
@@ -266,6 +273,35 @@ bool CanToggleAudioMute(content::WebContents* contents) {
   return false;
 }
 
+// Only run when cause should be rate limited (i.e. extensions)
+void updateTokenBuckets(content::WebContents* contents) {

[miu, 2015/07/16 00:28:26]

This function should be private, so please move it to inside the anonymous
namespace (above, before line 101).

+  DCHECK(contents);
+
+  LastMuteMetadata::CreateForWebContents(contents);  // Create if not exists.

[miu, 2015/07/16 00:28:26]

If this function is private, you could omit this call to CreateForWebContents(),
and just make sure to do it in SetTabAudioMuted() beforehand.

+
+  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) {

[miu, 2015/07/16 00:28:25]

This function should probably be private as well.  Your call.

+  DCHECK(contents);
+
+  LastMuteMetadata::CreateForWebContents(contents);  // Create if not exists.

[miu, 2015/07/16 00:28:26]

ditto: Also not needed if this function is private (see comment above).

+
+  return (LastMuteMetadata::FromWebContents(contents)->token_bucket <
+          base::TimeDelta::FromSeconds(kMuteTokenBucketCostSeconds));
+}
+
 const std::string& GetTabAudioMutedCause(content::WebContents* contents) {
   LastMuteMetadata::CreateForWebContents(contents);  // Create if not exists.
   if (GetTabMediaStateForContents(contents) == TAB_MEDIA_STATE_CAPTURING) {
@@ -276,16 +312,33 @@ 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;
+
+  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::CreateForWebContents(contents);  // Create if not exists.
   LastMuteMetadata::FromWebContents(contents)->cause = cause;
 
   contents->SetAudioMuted(mute);
+
+  return TAB_MUTED_RESULT_SUCCESS;
 }
 
 bool IsTabAudioMuted(content::WebContents* contents) {