Add UMA histogram about what format of swapchain is created for overlays

Ideally this should be YUY2, but we have a fallback to B8G8R8A8 and
should check that it's being used at most very rarely.

BUG=678800
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2799183002
Cr-Commit-Position: refs/heads/master@{#462738}

gpu/ipc/service/direct_composition_surface_win.cc

@@ -432,6 +432,8 @@ void DCLayerTree::SwapChainPresenter::ReallocateSwapChain() {
       d3d11_device_.get(), swap_chain_handle_.Get(), &desc, nullptr,
       swap_chain_.Receive());
 
+  bool yuy2_swapchain = true;
+
   if (FAILED(hr)) {
     // This should not be hit in production but is a simple fallback for
     // testing on systems without YUY2 swapchain support.
@@ -443,6 +445,7 @@ void DCLayerTree::SwapChainPresenter::ReallocateSwapChain() {
         d3d11_device_.get(), swap_chain_handle_.Get(), &desc, nullptr,
         swap_chain_.Receive());
     CHECK(SUCCEEDED(hr));
+    yuy2_swapchain = false;
   } else {
     // This is a sensible default colorspace for most videos.
     // TODO(jbauman): Use correct colorspace.
@@ -452,6 +455,8 @@ void DCLayerTree::SwapChainPresenter::ReallocateSwapChain() {
         DXGI_COLOR_SPACE_YCBCR_STUDIO_G22_LEFT_P709);
     CHECK(SUCCEEDED(hr));
   }
+  UMA_HISTOGRAM_BOOLEAN("GPU.DirectComposition.SwapchainFormat",
+                        yuy2_swapchain);
   out_view_.Reset();
 }
 

tools/metrics/histograms/histograms.xml

@@ -21871,6 +21871,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Whether or not a frame displays an overlay.</summary>
 </histogram>
 
+<histogram name="GPU.DirectComposition.SwapchainFormat" enum="SwapchainFormat">
+  <owner>jbauman@chromium.org</owner>
+  <summary>What type of swapchain was actually created for an overlay.</summary>
+</histogram>
+
 <histogram name="GPU.DoLinkProgramTime" units="ms">
   <owner>jmadill@chromium.org</owner>
   <summary>
@@ -113019,6 +113024,11 @@ from previous Chrome versions.
   <int value="3" label="Attempted"/>
 </enum>
 
+<enum name="SwapchainFormat" type="int">
+  <int value="0" label="B8G8R8A8"/>
+  <int value="1" label="YUY2"/>
+</enum>
+
 <enum name="SwReporterRunningTimeRegistryError" type="int">
   <int value="0" label="No error"/>
   <int value="1" label="Registry key invalid"/>