Refactor device scale factor on Mac and fix CoreAnimation bug

content/browser/renderer_host/compositing_iosurface_layer_mac.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/compositing_iosurface_layer_mac.h"
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <OpenGL/gl.h>
 
 #include "base/mac/sdk_forward_declarations.h"
@@ skipping 23 matching lines @@
     context_ = content::CompositingIOSurfaceContext::Get(
         content::CompositingIOSurfaceContext::kOffscreenContextWindowNumber);
     DCHECK(context_);
     needsDisplay_ = NO;
 
     ScopedCAActionDisabler disabler;
     [self setBackgroundColor:CGColorGetConstantColor(kCGColorWhite)];
     [self setContentsGravity:kCAGravityTopLeft];
     [self setFrame:NSRectToCGRect(
         [renderWidgetHostView_->cocoa_view() bounds])];
+    if ([self respondsToSelector:(@selector(setContentsScale:))]) {
+      [self setContentsScale:
+          renderWidgetHostView_->backing_store_scale_factor_];
+    }
     [self setNeedsDisplay];
-    [self updateScaleFactor];
   }
   return self;
 }
 
-- (void)updateScaleFactor {
-  if (!renderWidgetHostView_ ||
-      ![self respondsToSelector:(@selector(contentsScale))] ||
-      ![self respondsToSelector:(@selector(setContentsScale:))])
-    return;
-
-  float current_scale_factor = [self contentsScale];
-  float new_scale_factor = current_scale_factor;
-  if (renderWidgetHostView_->compositing_iosurface_) {
-    new_scale_factor =
-        renderWidgetHostView_->compositing_iosurface_->scale_factor();
-  }
-
-  if (new_scale_factor == current_scale_factor)
-    return;
-
-  ScopedCAActionDisabler disabler;
-  [self setContentsScale:new_scale_factor];
-}
-
 - (void)disableCompositing{
   ScopedCAActionDisabler disabler;
   [self removeFromSuperlayer];
   renderWidgetHostView_ = nil;
 }
 
 - (void)gotNewFrame {
   if (![self isAsynchronous]) {
     [self setNeedsDisplay];
     [self setAsynchronous:YES];
@@ skipping 111 matching lines @@
         false)) {
     renderWidgetHostView_->GotAcceleratedCompositingError();
     return;
   }
 
   needsDisplay_ = NO;
   renderWidgetHostView_->SendPendingLatencyInfoToHost();
 }
 
 @end