Properly remove the "needs attention" indicator for purged tabs.

If the resource coordinator purges a tab, the contents for that
tab will be destroyed after it is removed from the tabstrip.
Watch the tabstrip to make sure to handle that case.

BUG=786178
TEST=as in that case

Change-Id: I3d2c2e9fab29fe639615eed330ca769243c9a8f7
Reviewed-on: https://chromium-review.googlesource.com/777470Reviewed-by: Sidney San Martín <sdy@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517907}

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.cc

@@ -56,6 +56,7 @@ enum class JavaScriptDialogTabHelper::DismissalCause {
   BROWSER_SWITCHED = 5,
   DIALOG_BUTTON_CLICKED = 6,
   TAB_NAVIGATED = 7,
+  TAB_SWITCHED_OUT = 8,
   MAX,
 };
 
@@ -283,6 +284,21 @@ void JavaScriptDialogTabHelper::OnBrowserSetLastActive(Browser* browser) {
     HandleTabSwitchAway(DismissalCause::BROWSER_SWITCHED);
   }
 }
+
+void JavaScriptDialogTabHelper::TabReplacedAt(
+    TabStripModel* tab_strip_model,
+    content::WebContents* old_contents,
+    content::WebContents* new_contents,
+    int index) {
+  if (old_contents == WebContentsObserver::web_contents()) {
+    // At this point, this WebContents is no longer in the tabstrip. The usual
+    // teardown will not be able to turn off the attention indicator, so that
+    // must be done here.
+    SetTabNeedsAttentionImpl(false, tab_strip_model, index);
+
+    CloseDialog(DismissalCause::TAB_SWITCHED_OUT, false, base::string16());
+  }
+}
 #endif
 
 void JavaScriptDialogTabHelper::LogDialogDismissalCause(
@@ -347,8 +363,10 @@ void JavaScriptDialogTabHelper::CloseDialog(DismissalCause cause,
     std::move(dialog_callback_).Run(success, user_input);
 
   // If there's a pending dialog, then the tab is still in the "needs attention"
-  // state; clear it out.
-  if (pending_dialog_)
+  // state; clear it out. However, if the tab was switched out, the turning off
+  // of the "needs attention" state was done in TabReplacedAt() because
+  // SetTabNeedsAttention won't work, so don't call it.
+  if (pending_dialog_ && cause != DismissalCause::TAB_SWITCHED_OUT)
     SetTabNeedsAttention(false);
 
   dialog_.reset();
@@ -364,9 +382,23 @@ void JavaScriptDialogTabHelper::SetTabNeedsAttention(bool attention) {
 #if !defined(OS_ANDROID)
   content::WebContents* web_contents = WebContentsObserver::web_contents();
   Browser* browser = chrome::FindBrowserWithWebContents(web_contents);
-  DCHECK(browser);
-  browser->tab_strip_model()->SetTabNeedsAttentionAt(
-      browser->tab_strip_model()->GetIndexOfWebContents(web_contents),
-      attention);
+  TabStripModel* tab_strip_model = browser->tab_strip_model();
+
+  SetTabNeedsAttentionImpl(
+      attention, tab_strip_model,
+      tab_strip_model->GetIndexOfWebContents(web_contents));
 #endif
 }
+
+#if !defined(OS_ANDROID)
+void JavaScriptDialogTabHelper::SetTabNeedsAttentionImpl(
+    bool attention,
+    TabStripModel* tab_strip_model,
+    int index) {
+  tab_strip_model->SetTabNeedsAttentionAt(index, attention);
+  if (attention)
+    tab_strip_model->AddObserver(this);
+  else
+    tab_strip_model->RemoveObserver(this);
+}
+#endif

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h

@@ -18,6 +18,7 @@
 
 #if !defined(OS_ANDROID)
 #include "chrome/browser/ui/browser_list_observer.h"
+#include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
 #endif
 
 // A class, attached to WebContentses in browser windows, that is the
@@ -43,6 +44,7 @@ class JavaScriptDialogTabHelper
       public content::WebContentsObserver,
 #if !defined(OS_ANDROID)
       public chrome::BrowserListObserver,
+      public TabStripModelObserver,
 #endif
       public content::WebContentsUserData<JavaScriptDialogTabHelper> {
  public:
@@ -81,6 +83,12 @@ class JavaScriptDialogTabHelper
 #if !defined(OS_ANDROID)
   // BrowserListObserver:
   void OnBrowserSetLastActive(Browser* browser) override;
+
+  // TabStripModelObserver:
+  void TabReplacedAt(TabStripModel* tab_strip_model,
+                     content::WebContents* old_contents,
+                     content::WebContents* new_contents,
+                     int index) override;
 #endif
 
  private:
@@ -99,9 +107,17 @@ class JavaScriptDialogTabHelper
                    bool success,
                    const base::string16& user_input);
 
-  // Marks the tab as needing attention.
+  // Marks the tab as needing attention. The WebContents must be in a browser
+  // window.
   void SetTabNeedsAttention(bool attention);
 
+#if !defined(OS_ANDROID)
+  // Marks the tab as needing attention.
+  void SetTabNeedsAttentionImpl(bool attention,
+                                TabStripModel* tab_strip_model,
+                                int index);
+#endif
+
   // There can be at most one dialog (pending or not) being shown at any given
   // time on a tab. Depending on the type of the dialog, the variables
   // |dialog_|, |pending_dialog_|, and |dialog_callback_| can be present in

tools/metrics/histograms/enums.xml

@@ -22574,6 +22574,10 @@ Called by update_gpu_driver_bug_workaround_entries.py.-->
   <int value="7" label="Tab navigated">
     The user navigated the tab (e.g. back/forward, reload)
   </int>
+  <int value="8" label="Tab switched out">
+    The page displaying the dialog was switched out of its tab (e.g. tab
+    discarding)
+  </int>
 </enum>
 
 <enum name="JumplisticonsDeleteCategory">