Record whether and why the media default controls are being shown.

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
index 94a7462aa3d18fe965aef3720517b3e66fc8ae9d..1b616ce8902e0b6e38e3c1b84c43cbf55d973910 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -111,6 +111,14 @@ namespace {
 // URL protocol used to signal that the media source API is being used.
 const char mediaSourceBlobProtocol[] = "blob";
 
+enum MediaControlsShow {
+    MediaControlsShowAttribute = 0,
+    MediaControlsShowFullscreen,
+    MediaControlsShowNoScript,
+    MediaControlsShowNone,

[philipj_slow, 2016/02/19 04:05:43]

Maybe MediaControlsNotShown?

[mlamouri (slow - plz ping), 2016/02/23 18:42:13]

Done.

+    MediaControlsShowMax

[philipj_slow, 2016/02/19 04:05:43]

AutoplayExperimentHelper.h has NumberOfAutoplayMetrics, unless that's a weird
exception being consistent with that would be nice. UseCounter's
NumberOfFeatures is also familiar to me.

[mlamouri (slow - plz ping), 2016/02/23 18:42:13]

Yes, it is a weird exception, see:
https://code.google.com/p/chromium/codesearch#search/&q=%22DEFINE_STATIC_LOCA...

[philipj_slow, 2016/02/24 09:54:33]

OK, there's a bit of both, and some *Count as well.

+};
+
 #if !LOG_DISABLED
 String urlForLoggingMedia(const KURL& url)
 {
@@ -2083,17 +2091,7 @@ void HTMLMediaElement::setLoop(bool b)
 
 bool HTMLMediaElement::shouldShowControls() const
 {
-    LocalFrame* frame = document().frame();
-
-    // always show controls when scripting is disabled
-    if (frame && !frame->script().canExecuteScripts(NotAboutToExecuteScript))
-        return true;
-
-    // Always show controls when in full screen mode.
-    if (isFullscreen())
-        return true;
-
-    return fastHasAttribute(controlsAttr);
+    return shouldShowControlsInternal(false);
 }
 
 double HTMLMediaElement::volume() const
@@ -3353,7 +3351,8 @@ void HTMLMediaElement::configureMediaControls()
 
     ensureMediaControls();
     mediaControls()->reset();
-    if (shouldShowControls())
+
+    if (shouldShowControlsInternal(true))
         mediaControls()->show();
     else
         mediaControls()->hide();
@@ -3575,6 +3574,39 @@ void HTMLMediaElement::triggerAutoplayViewportCheckForTesting()
     m_autoplayHelper.triggerAutoplayViewportCheckForTesting();
 }
 
+bool HTMLMediaElement::shouldShowControlsInternal(bool record) const
+{
+    DEFINE_STATIC_LOCAL(EnumerationHistogram, showControlsHistogram, ("Media.Controls.Show", MediaControlsShowMax));
+
+    // These checks are in order of conditions superseeding each other, which

[philipj_slow, 2016/02/19 04:05:43]

Well, this would be true of any order where all "return true" are before the
"return false". The actual reason for the order is the expected frequency of
each case, with the most frequent cause first.

[mlamouri (slow - plz ping), 2016/02/23 18:42:13]

I understand what you mean. I guess my comment is confusing. I simply removed
it.

+    // also matches speed. In other words, a media element with a controls
+    // attribute, will always have controls, regardless of the other conditions.
+    // Same for an element in fullscreen. That means that recorded metrics will
+    // only show the superseeding reason of the controls showing.
+
+    if (fastHasAttribute(controlsAttr)) {
+        if (record)
+            showControlsHistogram.count(MediaControlsShowAttribute);
+        return true;
+    }
+
+    if (isFullscreen()) {
+        if (record)
+            showControlsHistogram.count(MediaControlsShowFullscreen);
+        return true;
+    }
+
+    LocalFrame* frame = document().frame();
+    if (frame && !frame->script().canExecuteScripts(NotAboutToExecuteScript)) {
+        if (record)
+            showControlsHistogram.count(MediaControlsShowNoScript);
+        return true;
+    }
+
+    showControlsHistogram.count(MediaControlsShowNone);
+    return false;
+}
+
 void HTMLMediaElement::clearWeakMembers(Visitor* visitor)
 {
     if (!Heap::isHeapObjectAlive(m_audioSourceNode))