[Local Screen Casting] Do not try to get the primary display when no displays

This CL makes WiredDisplayMediaRouteProvider not check for the primary display when there is 0 or 1 display.
This should fix the crash in which WDMRP attempts to get the primary display when the primary display ID is invalid.

Bug: 803881
Change-Id: I095ff7a69b1777c3466d2b6378fcd95e497c5641
Reviewed-on: https://chromium-review.googlesource.com/895389Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533760}

chrome/browser/media/router/providers/wired_display/wired_display_media_route_provider.cc

@@ -331,6 +331,11 @@ std::vector<MediaSinkInternal> WiredDisplayMediaRouteProvider::GetSinks()
 std::vector<Display> WiredDisplayMediaRouteProvider::GetAvailableDisplays()
     const {
   std::vector<Display> displays = GetAllDisplays();
+  // If there is only one display, the user should not be able to present to it.
+  // If there are no displays, GetPrimaryDisplay() below fails.
+  if (displays.size() <= 1)
+    return std::vector<Display>();
+
   const Display primary_display = GetPrimaryDisplay();
   std::sort(
       displays.begin(), displays.end(),
@@ -345,7 +350,8 @@ std::vector<Display> WiredDisplayMediaRouteProvider::GetAvailableDisplays()
     return display.id() != primary_display.id() &&
            display.bounds() == primary_display.bounds();
   });
-  // If there is only one display, the user should not be able to present to it.
+  // If all the displays are mirrored, the user should not be able to present to
+  // them.
   return displays.size() == 1 ? std::vector<Display>() : displays;
 }
 

chrome/browser/media/router/providers/wired_display/wired_display_media_route_provider_unittest.cc

@@ -128,6 +128,8 @@ class TestWiredDisplayMediaRouteProvider
     primary_display_ = std::move(primary_display);
   }
 
+  MOCK_CONST_METHOD0(GetPrimaryDisplayInternal, void());
+
  protected:
   // In the actual class, this method returns display::Screen::GetAllDisplays().
   // TODO(takumif): Expand display::test::TestScreen to support multiple
@@ -138,7 +140,10 @@ class TestWiredDisplayMediaRouteProvider
 
   // In the actual class, this method returns
   // display::Screen::GetPrimaryDisplay().
-  Display GetPrimaryDisplay() const override { return primary_display_; }
+  Display GetPrimaryDisplay() const override {
+    GetPrimaryDisplayInternal();
+    return primary_display_;
+  }
 
  private:
   std::vector<Display> all_displays_;
@@ -269,6 +274,20 @@ TEST_F(WiredDisplayMediaRouteProviderTest, NotifyOnDisplayChange) {
   base::RunLoop().RunUntilIdle();
 }
 
+TEST_F(WiredDisplayMediaRouteProviderTest, NoDisplay) {
+  provider_->StartObservingMediaSinks(kPresentationSource);
+  provider_->set_all_displays({primary_display_});
+  provider_->OnDisplayAdded(primary_display_);
+  base::RunLoop().RunUntilIdle();
+
+  // When the display list is empty, |provider_| should not try to get the
+  // primary display, as it would be invalid.
+  EXPECT_CALL(*provider_, GetPrimaryDisplayInternal()).Times(0);
+  provider_->set_all_displays({});
+  provider_->OnDisplayRemoved(primary_display_);
+  base::RunLoop().RunUntilIdle();
+}
+
 TEST_F(WiredDisplayMediaRouteProviderTest, NoSinksForNonPresentationSource) {
   EXPECT_CALL(router_,
               OnSinksReceived(kProviderId, kNonPresentationSource, _, _))