Prevent display going to sleep while taking a screenshot

On MacOS, GrabViewSnapshot() call would block for the duration of
display/GPU sleep which leads to protocol client to wait and tests
to time out when power saving is engaged. This prevents power saving
while there are pending screenshot requests.

BUG=599776

Review-Url: https://codereview.chromium.org/2044783002
Cr-Commit-Position: refs/heads/master@{#398245}

content/browser/renderer_host/render_widget_host_impl.cc

@@ -82,6 +82,8 @@
 #include "ui/snapshot/snapshot.h"
 
 #if defined(OS_MACOSX)
+#include "content/public/browser/power_save_blocker.h"
+#include "content/public/browser/power_save_blocker_factory.h"
 #include "ui/accelerated_widget_mac/window_resize_helper_mac.h"
 #endif
 
@@ -1284,6 +1286,20 @@ void RenderWidgetHostImpl::NotifyScreenInfoChanged() {
 void RenderWidgetHostImpl::GetSnapshotFromBrowser(
     const GetSnapshotFromBrowserCallback& callback) {
   int id = next_browser_snapshot_id_++;
+
+#if defined(OS_MACOSX)
+  // MacOS version of underlying GrabViewSnapshot() blocks while
+  // display/GPU are in a power-saving mode, so make sure display
+  // does not go to sleep for the duration of reading a snapshot.
+  if (pending_browser_snapshots_.empty()) {
+    DCHECK(!power_save_blocker_);
+    power_save_blocker_.reset(
+        CreatePowerSaveBlocker(
+            PowerSaveBlocker::kPowerSaveBlockPreventDisplaySleep,
+            PowerSaveBlocker::kReasonOther, "GetSnapshot")
+            .release());
+  }
+#endif
   pending_browser_snapshots_.insert(std::make_pair(id, callback));
   Send(new ViewMsg_ForceRedraw(GetRoutingID(), id));
 }
@@ -2143,6 +2159,10 @@ void RenderWidgetHostImpl::OnSnapshotDataReceived(int snapshot_id,
         ++it;
       }
   }
+#if defined(OS_MACOSX)
+  if (pending_browser_snapshots_.empty())
+    power_save_blocker_.reset();
+#endif
 }
 
 void RenderWidgetHostImpl::OnSnapshotDataReceivedAsync(

content/browser/renderer_host/render_widget_host_impl.h

@@ -87,6 +87,10 @@ struct EditCommand;
 struct ResizeParams;
 struct TextInputState;
 
+#if defined(OS_MACOSX)
+class PowerSaveBlocker;
+#endif
+
 // This implements the RenderWidgetHost interface that is exposed to
 // embedders of content, and adds things only visible to content.
 class CONTENT_EXPORT RenderWidgetHostImpl : public RenderWidgetHost,
@@ -821,6 +825,10 @@ class CONTENT_EXPORT RenderWidgetHostImpl : public RenderWidgetHost,
   // renderer process before clearing any previously displayed content.
   base::TimeDelta new_content_rendering_delay_;
 
+#if defined(OS_MACOSX)
+  std::unique_ptr<PowerSaveBlocker> power_save_blocker_;
+#endif
+
   base::WeakPtrFactory<RenderWidgetHostImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);