Allow to invoke a read-back while a view is visible only.

We should allow, the read back while view is active and hold
the frame till, readback gets processed. Dont process a
readback request when the view is hidden.

BUG=376769

Review URL: https://codereview.chromium.org/418853002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285488 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/render_widget_host_view_android.cc

@@ -300,7 +300,13 @@ void RenderWidgetHostViewAndroid::GetScaledContentBitmap(
     SkColorType color_type,
     gfx::Rect src_subrect,
     const base::Callback<void(bool, const SkBitmap&)>& result_callback) {
+  if (!host_ || host_->is_hidden()) {
+    result_callback.Run(false, SkBitmap());
+    return;
+  }
   if (!IsSurfaceAvailableForCopy()) {
+    // TODO(Sikugu): allow a read-back request to wait for a first frame if it
+    // was invoked while no frame was received yet
     result_callback.Run(false, SkBitmap());
     return;
   }
@@ -713,7 +719,8 @@ void RenderWidgetHostViewAndroid::CopyFromCompositingSurface(
     const gfx::Size& dst_size,
     const base::Callback<void(bool, const SkBitmap&)>& callback,
     const SkColorType color_type) {
-  if (!IsReadbackConfigSupported(color_type)) {
+  if ((!host_ || host_->is_hidden()) ||
+      !IsReadbackConfigSupported(color_type)) {
     callback.Run(false, SkBitmap());
     return;
   }