Disable back button when stack is empty

chrome/browser/android/vr_shell/textures/url_bar_texture.cc

 // Copyright 2017 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/android/vr_shell/textures/url_bar_texture.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "cc/paint/skia_paint_canvas.h"
 #include "chrome/browser/android/vr_shell/color_scheme.h"
 #include "chrome/browser/android/vr_shell/textures/render_text_wrapper.h"
@@ skipping 88 matching lines @@
       failure_callback_(failure_callback) {}
 
 UrlBarTexture::~UrlBarTexture() = default;
 
 void UrlBarTexture::SetURL(const GURL& gurl) {
   if (gurl_ != gurl)
     set_dirty();
   gurl_ = gurl;
 }
 
+void UrlBarTexture::SetHistoryButtonsEnabled(bool can_go_back,
+                                             bool can_go_forward) {
+  // Note: We don't have a forward button in the URL bar.

[cjgrant, 2017/05/29 16:12:25]

Comment disappears with the arg.

[ymalik, 2017/05/29 17:34:10]

Done.

+  if (can_go_back != can_go_back_)
+    set_dirty();
+  can_go_back_ = can_go_back;
+}
+
 void UrlBarTexture::SetSecurityLevel(SecurityLevel level) {
   if (security_level_ != level)
     set_dirty();
   security_level_ = level;
 }
 
 float UrlBarTexture::ToPixels(float meters) const {
   return meters * size_.width() / kWidth;
 }
 
@@ skipping 50 matching lines @@
 
   // Make a gfx canvas to support utility drawing methods.
   cc::SkiaPaintCanvas paint_canvas(canvas);
   gfx::Canvas gfx_canvas(&paint_canvas, 1.0f);
 
   // Back button area.
   SkRRect round_rect;
   SkVector rounded_corner = {kHeight / 2, kHeight / 2};
   SkVector left_corners[4] = {rounded_corner, {0, 0}, {0, 0}, rounded_corner};
   round_rect.setRectRadii({0, 0, kHeight, kHeight}, left_corners);
-  SkColor color =
-      hovered_ ? color_scheme().background_hover : color_scheme().background;
-  color = pressed_ ? color_scheme().background_down : color;
+  SkColor color = color_scheme().background;
+  if (can_go_back_) {

[cjgrant, 2017/05/29 16:12:25]

Can we kill the ternaries here?  This would read way easier with just if, else
if, else if, else, IMO.

[ymalik, 2017/05/29 17:34:10]

Done.

[ymalik, 2017/05/29 17:34:10]

Done.

+    color =
+        hovered_ ? color_scheme().background_hover : color_scheme().background;
+    color = pressed_ ? color_scheme().background_down : color;
+  }
   SkPaint paint;
   paint.setColor(color);
   canvas->drawRRect(round_rect, paint);
 
   // URL area.
   paint.setColor(color_scheme().background);
   SkVector right_corners[4] = {{0, 0}, rounded_corner, rounded_corner, {0, 0}};
   round_rect.setRectRadii({kHeight, 0, kWidth, kHeight}, right_corners);
   canvas->drawRRect(round_rect, paint);
 
   // Back button / URL separator vertical line.
   paint.setColor(color_scheme().separator);
   canvas->drawRect(SkRect::MakeXYWH(kHeight, 0, kSeparatorWidth, kHeight),
                    paint);
 
   // Back button icon.
   canvas->save();
   canvas->translate(kHeight / 2 + kBackIconOffset, kHeight / 2);
   canvas->translate(-kBackIconHeight / 2, -kBackIconHeight / 2);
   int icon_default_height = GetDefaultSizeOfVectorIcon(ui::kBackArrowIcon);
   float icon_scale = kBackIconHeight / icon_default_height;
   canvas->scale(icon_scale, icon_scale);
-  PaintVectorIcon(&gfx_canvas, ui::kBackArrowIcon, color_scheme().foreground);
+  PaintVectorIcon(
+      &gfx_canvas, ui::kBackArrowIcon,
+      can_go_back_ ? color_scheme().foreground : color_scheme().deemphasized);

[cjgrant, 2017/05/29 16:12:25]

deemphasized is a URL text color, right?  Shouldn't we have a separate color for
inactive buttons?  Seems like we shouldn't tie these together.

[ymalik, 2017/05/29 17:34:10]

Yeah was just here as placeholder. Posted hoverboard-dev for color and updated
with the correct value. 

   canvas->restore();
 
   // Site security state icon.
   if (!gurl_.is_empty()) {
     canvas->save();
     canvas->translate(
         kBackButtonWidth + kSeparatorWidth + kSecurityFieldWidth / 2,
         kHeight / 2);
     canvas->translate(-kSecurityIconHeight / 2, -kSecurityIconHeight / 2);
     const gfx::VectorIcon& icon = getSecurityIcon(security_level_);
@@ skipping 120 matching lines @@
 
 gfx::Size UrlBarTexture::GetPreferredTextureSize(int maximum_width) const {
   return gfx::Size(maximum_width, maximum_width * kHeight / kWidth);
 }
 
 gfx::SizeF UrlBarTexture::GetDrawnSize() const {
   return size_;
 }
 
 }  // namespace vr_shell