Disable back button when stack is empty

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

Index: chrome/browser/android/vr_shell/textures/url_bar_texture.cc
diff --git a/chrome/browser/android/vr_shell/textures/url_bar_texture.cc b/chrome/browser/android/vr_shell/textures/url_bar_texture.cc
index 5ebf629b929b4380a87abc9d1b76e09d4c4dbe4f..308d155544b14652086c0fee91b823f9835c6ae2 100644
--- a/chrome/browser/android/vr_shell/textures/url_bar_texture.cc
+++ b/chrome/browser/android/vr_shell/textures/url_bar_texture.cc
@@ -106,6 +106,14 @@ void UrlBarTexture::SetURL(const GURL& gurl) {
   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();
@@ -176,9 +184,12 @@ void UrlBarTexture::Draw(SkCanvas* canvas, const gfx::Size& texture_size) {
   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);
@@ -201,7 +212,9 @@ void UrlBarTexture::Draw(SkCanvas* canvas, const gfx::Size& texture_size) {
   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.