Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/ui/cocoa/tabs/tab_window_controller.mm

Index: chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
diff --git a/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm b/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
index 716cb70c975cf3dc0740bb3958365f211f1b17d3..b81b80f40565f32ff0be9e093de162652b86bcf0 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_window_controller.mm
@@ -6,6 +6,8 @@
 
 #include "base/logging.h"
 #import "base/mac/sdk_forward_declarations.h"
+#include "base/memory/ptr_util.h"
+#include "chrome/browser/ui/browser_view_histogram_helper.h"
 #import "chrome/browser/ui/cocoa/browser_window_layout.h"
 #import "chrome/browser/ui/cocoa/fast_resize_view.h"
 #import "chrome/browser/ui/cocoa/framed_browser_window.h"
@@ -64,13 +66,23 @@
 @end
 
 // Subview of the window's contentView, contains everything but the tab strip.
-@interface ChromeContentView : NSView
+@interface ChromeContentView : NSView {
+ @private
+  std::unique_ptr<BrowserViewHistogramHelper> histogram_helper_;
+}
 @end
 
 @implementation ChromeContentView
 
 // NSView overrides.
 
+- (instancetype)initWithFrame:(NSRect)frameRect {
+  if ((self = [super initWithFrame:frameRect])) {
+    histogram_helper_ = base::MakeUnique<BrowserViewHistogramHelper>();
+  }
+  return self;
+}
+
 // Since Auto Layout and frame-based layout behave differently in small but
 // important ways (e.g. Auto Layout can restrict window resizing, frame-based
 // layout doesn't log a warning when a view's autoresizing mask can't be
@@ -79,6 +91,13 @@
   return YES;
 }
 
+- (void)drawRect:(NSRect)dirtyRect {
+  // -drawRect: is called from -drawLayer:inContext:, which is called before all
+  // ChromeContentView's got a chance to paint. But there seems to be no
+  // non-hacky way of getting that notification.
+  histogram_helper_->OnDidPaintChildren(nullptr);
+}
+
 @end
 
 @implementation TabWindowController