Disable back button when stack is empty

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

Index: chrome/browser/android/vr_shell/textures/url_bar_texture.h
diff --git a/chrome/browser/android/vr_shell/textures/url_bar_texture.h b/chrome/browser/android/vr_shell/textures/url_bar_texture.h
index 2a6d4b81f75cb2c2378a3a0275ef6467314d829b..cbf215a8e7065da1a96a0bd2b77092dd2c476889 100644
--- a/chrome/browser/android/vr_shell/textures/url_bar_texture.h
+++ b/chrome/browser/android/vr_shell/textures/url_bar_texture.h
@@ -39,6 +39,7 @@ class UrlBarTexture : public UiTexture {
   gfx::SizeF GetDrawnSize() const override;
 
   void SetURL(const GURL& gurl);
+  void SetHistoryButtonsEnabled(bool can_go_back, bool can_go_forward);

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

Since the texture only supports back, why not drop forward here?

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

I figured that it may at some point, so plumbed through, but its probably okay
to remove. DOne.

   void SetSecurityLevel(security_state::SecurityLevel level);
 
   bool HitsBackButton(const gfx::PointF& position) const;
@@ -65,6 +66,7 @@ class UrlBarTexture : public UiTexture {
   gfx::SizeF size_;
   bool hovered_ = false;
   bool pressed_ = false;
+  bool can_go_back_ = false;
 
   GURL gurl_;
   security_state::SecurityLevel security_level_;