gpu: Fix AsyncSwapBuffer tracing.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 6934e8bc58baacbe074b94a54cc01b6e8f939737..ad682ede98c6e7deb2aa2a3600661878d36f967f 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -926,6 +926,7 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
                                        const volatile GLint* rects);
 
   // Callback for async SwapBuffers.
+  void FinishAsyncSwapBuffers(gfx::SwapResult result);
   void FinishSwapBuffers(gfx::SwapResult result);
 
   void DoCommitOverlayPlanes();
@@ -2371,6 +2372,8 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
   bool supports_swap_buffers_with_bounds_;
   bool supports_commit_overlay_planes_;
   bool supports_async_swap_;
+  uint32_t next_async_swap_id_ = 1;
+  uint32_t pending_swaps_ = 0;
   bool supports_dc_layers_ = false;
 
   // These flags are used to override the state of the shared feature_info_
@@ -11884,10 +11887,14 @@ error::Error GLES2DecoderImpl::HandlePostSubBufferCHROMIUM(
   ClearScheduleDCLayerState();
 
   if (supports_async_swap_) {
-    TRACE_EVENT_ASYNC_BEGIN0("cc", "GLES2DecoderImpl::AsyncSwapBuffers", this);
+    DCHECK_LT(pending_swaps_, 2u);
+    uint32_t async_swap_id = next_async_swap_id_++;
+    ++pending_swaps_;
+    TRACE_EVENT_ASYNC_BEGIN0("gpu", "AsyncSwapBuffers", async_swap_id);
+
     surface_->PostSubBufferAsync(
         c.x, c.y, c.width, c.height,
-        base::Bind(&GLES2DecoderImpl::FinishSwapBuffers,
+        base::Bind(&GLES2DecoderImpl::FinishAsyncSwapBuffers,
                    base::AsWeakPtr(this)));
   } else {
     FinishSwapBuffers(surface_->PostSubBuffer(c.x, c.y, c.width, c.height));
@@ -15505,9 +15512,13 @@ void GLES2DecoderImpl::DoSwapBuffers() {
         glFlush();
     }
   } else if (supports_async_swap_) {
-    TRACE_EVENT_ASYNC_BEGIN0("cc", "GLES2DecoderImpl::AsyncSwapBuffers", this);
-    surface_->SwapBuffersAsync(base::Bind(&GLES2DecoderImpl::FinishSwapBuffers,
-                                          base::AsWeakPtr(this)));
+    DCHECK_LT(pending_swaps_, 2u);
+    uint32_t async_swap_id = next_async_swap_id_++;
+    ++pending_swaps_;
+    TRACE_EVENT_ASYNC_BEGIN0("gpu", "AsyncSwapBuffers", async_swap_id);
+
+    surface_->SwapBuffersAsync(base::Bind(
+        &GLES2DecoderImpl::FinishAsyncSwapBuffers, base::AsWeakPtr(this)));
   } else {
     FinishSwapBuffers(surface_->SwapBuffers());
   }
@@ -15517,6 +15528,15 @@ void GLES2DecoderImpl::DoSwapBuffers() {
   ExitCommandProcessingEarly();
 }
 
+void GLES2DecoderImpl::FinishAsyncSwapBuffers(gfx::SwapResult result) {
+  DCHECK_NE(0u, pending_swaps_);
+  uint32_t async_swap_id = next_async_swap_id_ - pending_swaps_;
+  --pending_swaps_;
+  TRACE_EVENT_ASYNC_END0("gpu", "AsyncSwapBuffers", async_swap_id);
+
+  FinishSwapBuffers(result);
+}
+
 void GLES2DecoderImpl::FinishSwapBuffers(gfx::SwapResult result) {
   if (result == gfx::SwapResult::SWAP_FAILED) {
     LOG(ERROR) << "Context lost because SwapBuffers failed.";
@@ -15531,10 +15551,6 @@ void GLES2DecoderImpl::FinishSwapBuffers(gfx::SwapResult result) {
     // known values.
     backbuffer_needs_clear_bits_ |= GL_COLOR_BUFFER_BIT;
   }
-
-  if (supports_async_swap_) {
-    TRACE_EVENT_ASYNC_END0("cc", "GLES2DecoderImpl::AsyncSwapBuffers", this);
-  }
 }
 
 void GLES2DecoderImpl::DoCommitOverlayPlanes() {