[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 f16150b1b94e39e016b05eb26c50b8824565e431..ead104c7eaf256efa39dce954633b30c8d31d5ae 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"
@@ -46,7 +47,7 @@ static const char kJpeg[] = "jpeg";
 static int kDefaultScreenshotQuality = 80;
 static int kFrameRetryDelayMs = 100;
 static int kCaptureRetryLimit = 2;
-static int kMaxScreencastFramesInFlight = 4;
+static int kMaxScreencastFramesInFlight = 2;
 
 void QueryUsageAndQuotaCompletedOnIOThread(
     const UsageAndQuotaQuery::Callback& callback,
@@ -477,31 +478,14 @@ 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(
-    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(kFrameRetryDelayMs));
-    }
-    return;
-  }
-
+static std::string EncodeScreencastFrame(const SkBitmap& bitmap,

[dgozman, 2014/11/20 14:23:05]

Let's move to the namespace at the top and remove static.

[vkuzkokov, 2014/11/20 14:55:27]

Done.

+                                         const std::string& format,
+                                         int quality) {
   std::vector<unsigned char> data;
   SkAutoLockPixels lock_image(bitmap);
   bool encoded;
@@ -525,15 +509,45 @@ void PageHandler::ScreencastFrameCaptured(
   }
 
   if (!encoded)
-    return;
+    return std::string();
 
   std::string base_64_data;
   base::Base64Encode(
       base::StringPiece(reinterpret_cast<char*>(&data[0]), data.size()),
       &base_64_data);
 
+  return 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(kFrameRetryDelayMs));
+    }
+    return;
+  }
+  base::PostTaskAndReplyWithResult(
+      base::WorkerPool::GetTaskRunner(true).get(),
+      FROM_HERE,
+      base::Bind(&EncodeScreencastFrame,
+                 bitmap, screencast_format_, screencast_quality_),
+      base::Bind(&PageHandler::ScreencastFrameEncoded,
+                 weak_factory_.GetWeakPtr(), metadata));
+}
+
+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_)
+  if (metadata.device_scale_factor == 0 || !host_ || data.empty())
     return;
 
   RenderWidgetHostViewBase* view = static_cast<RenderWidgetHostViewBase*>(
@@ -552,7 +566,7 @@ void PageHandler::ScreencastFrameCaptured(
           ->set_scroll_offset_x(metadata.root_scroll_offset.x())
           ->set_scroll_offset_y(metadata.root_scroll_offset.y());
   client_->ScreencastFrame(ScreencastFrameParams::Create()
-      ->set_data(base_64_data)
+      ->set_data(data)
       ->set_metadata(param_metadata)
       ->set_frame_number(++screencast_frame_sent_));
 }