mac: Add metrics for fullscreen entry.

chrome/browser/ui/cocoa/browser_window_controller_private.mm

Index: chrome/browser/ui/cocoa/browser_window_controller_private.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_controller_private.mm b/chrome/browser/ui/cocoa/browser_window_controller_private.mm
index 8dd4f36cd8f3e6637a4dc67edcc605b3db301b24..a28c8b0a966154c9280e70a32202826e6f3297df 100644
--- a/chrome/browser/ui/cocoa/browser_window_controller_private.mm
+++ b/chrome/browser/ui/cocoa/browser_window_controller_private.mm
@@ -10,6 +10,7 @@
 #include "base/mac/mac_util.h"
 #import "base/mac/scoped_nsobject.h"
 #import "base/mac/sdk_forward_declarations.h"
+#include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/browser_process.h"
@@ -50,6 +51,75 @@
 using content::RenderWidgetHostView;
 using content::WebContents;
 
+namespace {
+
+// Each time the user enters fullscreen, a single histogram enumeration is
+// recorded. There are several relevant parameters, whose values are mapped
+// directly into individual bits of the enumeration.
+//
+// + Fullscreen Mechanism: The mechanism by which the window's size is changed
+// to encompass the entire screen. Bit 0.
+//   - AppKit (value of bit: 1)
+//   - Immersive (value of bit: 0)
+//
+// + Primary Screen: Whether the window is located on the screen at index 0.
+// Depending on OSX version, this has different implications for menu bar
+// visibility. Bit 1.
+//   - Primary (value of bit: 1)
+//   - Secondary (value of bit: 0)
+//
+// + Displays have separate spaces: An option available in Mission Control in
+// OSX 10.9+. Bit 2.
+//   - On (value of bit: 1)
+//   - Off (value of bit: 0)
+//
+// + Multiple screens: Whether the user has multiple screens. If the window is
+// located on a secondary screen, then there must be multiple screens. Bit 3.
+//   - Yes (value of bit: 1)
+//   - No (value of bit: 0)
+
+enum FullscreenMechanism {
+  IMMERSIVE_FULLSCREEN_MECHANISM,
+  APPKIT_FULLSCREEN_MECHANISM,
+};
+
+enum {
+  FULLSCREEN_MECHANISM_BIT = 0,
+  PRIMARY_SCREEN_BIT = 1,
+  DISPLAYS_SEPARATE_SPACES_BIT = 2,
+  MULTIPLE_SCREENS_BIT = 3,
+  BIT_COUNT
+};
+
+// Emits a histogram entry indicating that |window| is being made fullscreen.
+void RecordFullscreenHistogram(FullscreenMechanism mechanism,
+                               NSWindow* window) {
+  NSArray* screens = [NSScreen screens];
+  bool primary_screen = ([[window screen] isEqual:[screens objectAtIndex:0]]);
+  bool displays_have_separate_spaces =
+      [NSScreen respondsToSelector:@selector(screensHaveSeparateSpaces)] &&
+      [NSScreen screensHaveSeparateSpaces];
+  bool multiple_screens = [screens count] > 1;
+
+  int output = 0;
+  if (mechanism == APPKIT_FULLSCREEN_MECHANISM)
+    output += 1 << FULLSCREEN_MECHANISM_BIT;
+
+  if (primary_screen)
+    output += 1 << PRIMARY_SCREEN_BIT;
+
+  if (displays_have_separate_spaces)
+    output += 1 << DISPLAYS_SEPARATE_SPACES_BIT;
+
+  if (multiple_screens)
+    output += 1 << MULTIPLE_SCREENS_BIT;
+
+  int max_output = 1 << BIT_COUNT;
+  UMA_HISTOGRAM_ENUMERATION("OSX.Fullscreen.Enter", output, max_output);
+}
+
+}  // namespace
+
 @implementation BrowserWindowController(Private)
 
 // Create the tab strip controller.
@@ -449,6 +519,8 @@ willPositionSheet:(NSWindow*)sheet
 }
 
 - (void)enterImmersiveFullscreen {
+  RecordFullscreenHistogram(IMMERSIVE_FULLSCREEN_MECHANISM, [self window]);
+
   // Set to NO by |-windowDidEnterFullScreen:|.
   enteringImmersiveFullscreen_ = YES;
 
@@ -601,6 +673,8 @@ willPositionSheet:(NSWindow*)sheet
 }
 
 - (void)windowWillEnterFullScreen:(NSNotification*)notification {
+  RecordFullscreenHistogram(APPKIT_FULLSCREEN_MECHANISM, [self window]);
+
   if (notification)  // For System Fullscreen when non-nil.
     [self registerForContentViewResizeNotifications];