[DevTools] Move PNG encoding from UI to worker thread.

content/browser/devtools/protocol/page_handler.cc

Index: content/browser/devtools/protocol/page_handler.cc
diff --git a/content/browser/devtools/protocol/page_handler.cc b/content/browser/devtools/protocol/page_handler.cc
index ec771aea83dcb1432732e4f2d131a384460d3e69..3c1bad86113a078edf6292dd6c295bbe6730b8dc 100644
--- a/content/browser/devtools/protocol/page_handler.cc
+++ b/content/browser/devtools/protocol/page_handler.cc
@@ -10,6 +10,7 @@
 #include "base/bind.h"
 #include "base/strings/string16.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/threading/worker_pool.h"
 #include "content/browser/devtools/protocol/color_picker.h"
 #include "content/browser/devtools/protocol/usage_and_quota_query.h"
 #include "content/browser/geolocation/geolocation_service_context.h"
@@ -476,31 +477,16 @@ void PageHandler::InnerSwapCompositorFrame() {
         snapshot_size_dip,
         base::Bind(&PageHandler::ScreencastFrameCaptured,
                    weak_factory_.GetWeakPtr(),
-                   screencast_format_,
-                   screencast_quality_,
                    last_compositor_frame_metadata_),
         kN32_SkColorType);
   }
 }
 
-void PageHandler::ScreencastFrameCaptured(
+static void EncodeScreencastFrame(
+    const SkBitmap& bitmap,
     const std::string& format,
     int quality,
-    const cc::CompositorFrameMetadata& metadata,
-    const SkBitmap& bitmap,
-    ReadbackResponse response) {
-  if (response != READBACK_SUCCESS) {
-    if (capture_retry_count_) {
-      --capture_retry_count_;
-      base::MessageLoop::current()->PostDelayedTask(
-          FROM_HERE,
-          base::Bind(&PageHandler::InnerSwapCompositorFrame,
-                     weak_factory_.GetWeakPtr()),
-          base::TimeDelta::FromMilliseconds(kFrameRateThresholdMs));
-    }
-    return;
-  }
-
+    const base::Callback<void(const std::string&)> callback) {
   std::vector<unsigned char> data;
   SkAutoLockPixels lock_image(bitmap);
   bool encoded;
@@ -531,6 +517,39 @@ void PageHandler::ScreencastFrameCaptured(
       base::StringPiece(reinterpret_cast<char*>(&data[0]), data.size()),
       &base_64_data);
 
+  BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
+                          base::Bind(callback, base_64_data));
+}
+
+void PageHandler::ScreencastFrameCaptured(
+    const cc::CompositorFrameMetadata& metadata,
+    const SkBitmap& bitmap,
+    ReadbackResponse response) {
+  if (response != READBACK_SUCCESS) {
+    if (capture_retry_count_) {
+      --capture_retry_count_;
+      base::MessageLoop::current()->PostDelayedTask(
+          FROM_HERE,
+          base::Bind(&PageHandler::InnerSwapCompositorFrame,
+                     weak_factory_.GetWeakPtr()),
+          base::TimeDelta::FromMilliseconds(kFrameRateThresholdMs));
+    }
+    return;
+  }
+  base::WorkerPool::PostTask(

[dgozman, 2014/11/17 14:03:59]

Maybe use PostTaskAndReply?

[vkuzkokov, 2014/11/17 14:47:47]

PostTaskAndReplyWithResult. Done.

+      FROM_HERE,
+      base::Bind(&EncodeScreencastFrame,
+                 bitmap,
+                 screencast_format_,

[dgozman, 2014/11/17 14:03:59]

We passed these as params for the case when e.g. format changed with next
protocol call.

[vkuzkokov, 2014/11/17 14:47:47]

This way we use more recent settings for format and quality.

+                 screencast_quality_,
+                 base::Bind(&PageHandler::ScreencastFrameEncoded,
+                            weak_factory_.GetWeakPtr(), metadata)),
+      true);
+}
+
+void PageHandler::ScreencastFrameEncoded(
+    const cc::CompositorFrameMetadata& metadata,
+    const std::string& data) {
   // Consider metadata empty in case it has no device scale factor.
   if (metadata.device_scale_factor == 0 || !host_)
     return;
@@ -564,7 +583,7 @@ void PageHandler::ScreencastFrameCaptured(
               ->set_width(metadata.scrollable_viewport_size.width())
               ->set_height(metadata.scrollable_viewport_size.height()));
   client_->ScreencastFrame(ScreencastFrameParams::Create()
-      ->set_data(base_64_data)
+      ->set_data(data)
       ->set_metadata(param_metadata));
 }