Fix partial screenshot/window screenshot when holding Alt+Tab.

ash/utility/screenshot_controller.cc

Index: ash/utility/screenshot_controller.cc
diff --git a/ash/utility/screenshot_controller.cc b/ash/utility/screenshot_controller.cc
index 64e4f99785f09fd729063fb9d05434708c248969..9bd71f8e442e9eab816b0fbdc6efa84146136299 100644
--- a/ash/utility/screenshot_controller.cc
+++ b/ash/utility/screenshot_controller.cc
@@ -12,7 +12,6 @@
 #include "ash/shell.h"
 #include "ash/wm/window_util.h"
 #include "base/memory/ptr_util.h"
-#include "ui/aura/client/capture_client.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window_targeter.h"
 #include "ui/compositor/paint_recorder.h"
@@ -62,17 +61,10 @@ class ScreenshotWindowTargeter : public aura::WindowTargeter {
 
     gfx::Point target_location = event->location();
     event->set_location(location);
-
-    // Ignore capture window when finding the target for located event.

[Evan Stade, 2016/10/06 16:32:34]

so I noticed this bit of code as well, which seems to also be dealing with
capture but in a different way. +oshima who wrote this. Do you remember what
this was intended to deal with? It seems unnecessary now if we just explicitly
break capture. Do you know what behavior I should test to make sure we're not
regressing something?

[oshima, 2016/10/06 20:07:53]

This is to deal with menu windows, so please do not remove.

-    aura::client::CaptureClient* original_capture_client =
-        aura::client::GetCaptureClient(root_window);
-    aura::client::SetCaptureClient(root_window, nullptr);
-
     aura::Window* selected =
         static_cast<aura::Window*>(FindTargetForEvent(root_window, event));
 
     // Restore State.
-    aura::client::SetCaptureClient(root_window, original_capture_client);
     event->set_location(target_location);
     return selected;
   }
@@ -255,15 +247,20 @@ void ScreenshotController::StartWindowScreenshotSession(
     DCHECK_EQ(screenshot_delegate_, screenshot_delegate);
     return;
   }
-  screenshot_delegate_ = screenshot_delegate;
-  mode_ = WINDOW;
 
-  display::Screen::GetScreen()->AddObserver(this);
   for (aura::Window* root : Shell::GetAllRootWindows()) {
+    // Since we'll be pre-handling all mouse events, break any existing
+    // captures.
+    aura::client::GetCaptureClient(root)->SetCapture(nullptr);
     layers_[root] = base::MakeUnique<ScreenshotLayer>(
         Shell::GetContainer(root, kShellWindowId_OverlayContainer)->layer(),
         true);
   }
+
+  screenshot_delegate_ = screenshot_delegate;
+  mode_ = WINDOW;
+
+  display::Screen::GetScreen()->AddObserver(this);
   SetSelectedWindow(wm::GetActiveWindow());
 
   cursor_setter_.reset(new ScopedCursorSetter(
@@ -281,15 +278,19 @@ void ScreenshotController::StartPartialScreenshotSession(
     return;
   }
 
-  screenshot_delegate_ = screenshot_delegate;
-  mode_ = PARTIAL;
-  display::Screen::GetScreen()->AddObserver(this);
   for (aura::Window* root : Shell::GetAllRootWindows()) {
+    // Since we'll be pre-handling all mouse events, break any existing
+    // captures.
+    aura::client::GetCaptureClient(root)->SetCapture(nullptr);
     layers_[root] = base::MakeUnique<ScreenshotLayer>(
         Shell::GetContainer(root, kShellWindowId_OverlayContainer)->layer(),
         draw_overlay_immediately);
   }
 
+  screenshot_delegate_ = screenshot_delegate;
+  mode_ = PARTIAL;
+  display::Screen::GetScreen()->AddObserver(this);
+
   if (!pen_events_only_) {
     cursor_setter_.reset(new ScopedCursorSetter(
         Shell::GetInstance()->cursor_manager(), ui::kCursorCross));