Fix pixelation of tab borders when device scale changes (alternate approach)

chrome/browser/ui/views/tabs/tab.cc

 // Copyright (c) 2012 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 "chrome/browser/ui/views/tabs/tab.h"
 
 #include <stddef.h>
 #include <limits>
 #include <utility>
 
@@ skipping 138 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // ImageCacheEntryMetadata
 //
 // All metadata necessary to uniquely identify a cached image.
 struct ImageCacheEntryMetadata {
   ImageCacheEntryMetadata(int resource_id,
                           SkColor fill_color,
                           SkColor stroke_color,
                           bool use_fill_and_stroke_images,
-                          ui::ScaleFactor scale_factor,
+                          float scale_factor,
                           const gfx::Size& size);
 
   ~ImageCacheEntryMetadata();
 
   bool operator==(const ImageCacheEntryMetadata& rhs) const;
 
   int resource_id;     // Only needed by pre-MD
   SkColor fill_color;  // Both colors only needed by MD
   SkColor stroke_color;
   bool use_fill_and_stroke_images;
-  ui::ScaleFactor scale_factor;
+  float scale_factor;
   gfx::Size size;
 };
 
 ImageCacheEntryMetadata::ImageCacheEntryMetadata(
     int resource_id,
     SkColor fill_color,
     SkColor stroke_color,
     bool use_fill_and_stroke_images,
-    ui::ScaleFactor scale_factor,
+    float scale_factor,
     const gfx::Size& size)
     : resource_id(resource_id),
       fill_color(fill_color),
       stroke_color(stroke_color),
       use_fill_and_stroke_images(use_fill_and_stroke_images),
       scale_factor(scale_factor),
       size(size) {
-  DCHECK_NE(ui::SCALE_FACTOR_NONE, scale_factor);
+  DCHECK_NE(0.0, scale_factor);

[Peter Kasting, 2016/08/15 23:07:39]

Nit: Technically 0.0 is a double.  Honestly I'd rather just ditch this DCHECK
since I believe scale 0 won't actually cause any problems in called code.

 
   // Some fields are only relevant for pre-MD vs. MD.  Erase the irrelevant ones
   // so they don't cause incorrect cache misses.
   // TODO(pkasting): Remove |resource_id| field when non-MD code is deleted.
   if (ui::MaterialDesignController::IsModeMaterial())
     resource_id = 0;
   else
     fill_color = stroke_color = SK_ColorTRANSPARENT;
 }
 
@@ skipping 1343 matching lines @@
   // really need to clip the stroke and not the fill (for stacked tabs).  This
   // saves memory and avoids an extra image draw at the cost of recalculating
   // the images when MaySetClip() toggles.
   const bool use_fill_and_stroke_images =
       controller_->MaySetClip() &&
       ui::MaterialDesignController::IsModeMaterial();
 
   const ImageCacheEntryMetadata metadata(
       fill_id, tp->GetColor(ThemeProperties::COLOR_BACKGROUND_TAB),
       controller_->GetToolbarTopSeparatorColor(), use_fill_and_stroke_images,
-      ui::GetSupportedScaleFactor(canvas->image_scale()), size());
+      canvas->image_scale(), size());
   auto it = std::find_if(
       g_image_cache->begin(), g_image_cache->end(),
       [&metadata](const ImageCacheEntry& e) { return e.metadata == metadata; });
   if (it == g_image_cache->end()) {
     gfx::Canvas tmp_canvas(size(), canvas->image_scale(), false);
     if (use_fill_and_stroke_images) {
       gfx::Canvas tmp_fill_canvas(size(), canvas->image_scale(), false);
       PaintTabBackgroundUsingFillId(&tmp_fill_canvas, &tmp_canvas, false,
                                     fill_id, false, y_offset);
       g_image_cache->emplace_front(
@@ skipping 297 matching lines @@
 gfx::Rect Tab::GetImmersiveBarRect() const {
   // The main bar is as wide as the normal tab's horizontal top line.
   // This top line of the tab extends a few pixels left and right of the
   // center image due to pixels in the rounded corner images.
   const int kBarPadding = 1;
   int main_bar_left = g_active_images.l_width - kBarPadding;
   int main_bar_right = width() - g_active_images.r_width + kBarPadding;
   return gfx::Rect(
       main_bar_left, 0, main_bar_right - main_bar_left, kImmersiveBarHeight);
 }