Plugin Power Saver: Add UI Overlay to throttled plugin using placeholder.

chrome/renderer/plugins/plugin_preroller.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/renderer/plugins/plugin_preroller.h"
+
+#include "base/base64.h"
+#include "chrome/grit/renderer_resources.h"
+#include "chrome/renderer/plugins/chrome_plugin_placeholder.h"
+#include "third_party/WebKit/public/platform/WebRect.h"
+#include "third_party/WebKit/public/web/WebElement.h"
+#include "third_party/WebKit/public/web/WebPlugin.h"
+#include "third_party/WebKit/public/web/WebPluginContainer.h"
+#include "ui/gfx/codec/png_codec.h"
+
+PluginPreroller::PluginPreroller(content::RenderFrame* render_frame,
+                                 blink::WebLocalFrame* frame,
+                                 const blink::WebPluginParams& params,
+                                 const content::WebPluginInfo& info,
+                                 const std::string& identifier,
+                                 const base::string16& name,
+                                 const base::string16& message,
+                                 blink::WebPlugin* plugin,
+                                 content::PluginInstanceThrottler* throttler)
+    : render_frame_(render_frame),
+      frame_(frame),
+      params_(params),
+      info_(info),
+      identifier_(identifier),
+      name_(name),
+      message_(message),
+      plugin_(plugin),
+      throttler_(throttler) {
+  DCHECK(plugin);
+  DCHECK(throttler);
+  throttler_->AddObserver(this);
+}
+
+PluginPreroller::~PluginPreroller() {
+  if (throttler_)
+    throttler_->RemoveObserver(this);
+}
+
+void PluginPreroller::OnKeyframeExtracted(const SkBitmap* bitmap) {
+  std::vector<unsigned char> png_data;
+  if (!gfx::PNGCodec::EncodeBGRASkBitmap(*bitmap, false, &png_data)) {
+    DLOG(ERROR) << "Provided keyframe could not be encoded as PNG.";
+  }
+
+  std::string png_as_string(reinterpret_cast<char*>(&png_data[0]),

[Bernhard Bauer, 2015/01/30 14:12:56]

If encoding the keyframe failed, the vector will be empty, so technically
accessing element 0 would already be out of bounds. Just return in that case?

[tommycli, 2015/01/30 17:02:40]

Done.

+                            png_data.size());
+
+  std::string data_url_header = "data:image/png;base64,";
+  std::string data_url_body;
+  base::Base64Encode(png_as_string, &data_url_body);

[Bernhard Bauer, 2015/01/30 14:12:56]

base::Base64Encode() takes a base::StringPiece, so if you want to prematurely
optimize things, you could construct a base::StringPiece and save one copy :D

[tommycli, 2015/01/30 17:02:40]

Done.

+  keyframe_data_url_ = data_url_header + data_url_body;
+}
+
+void PluginPreroller::OnThrottleStateChange() {
+  if (throttler_->IsThrottled()) {

[Bernhard Bauer, 2015/01/30 14:12:56]

Early-return if the throttler is not throttled? That decreases the indentation
level, and you could put |this| into a scoped_ptr and have it automatically be
destroyed when returning.

[tommycli, 2015/01/30 17:02:40]

Done. But I think I only want to destroy the preroller when it's throttled.

+    ChromePluginPlaceholder* placeholder =
+        ChromePluginPlaceholder::CreateBlockedPlugin(
+            render_frame_, frame_, params_, info_, identifier_, name_,
+            IDR_PLUGIN_POSTER_HTML, message_, GURL(keyframe_data_url_), plugin_,
+            throttler_);
+    placeholder->set_power_saver_mode(
+        content::PluginPowerSaverMode::POWER_SAVER_MODE_PERIPHERAL_THROTTLED);
+    placeholder->set_allow_loading(true);
+
+    // Set the new plug-in on the container before initializing it.

[Bernhard Bauer, 2015/01/30 14:12:56]

I don't think the order of calls is important anymore, although keeping the
order as it is probably won't hurt either. Maybe let's just remove the comment,
to not create the impression that the order matters?

[tommycli, 2015/01/30 17:02:40]

Done.

+    blink::WebPluginContainer* container = plugin_->container();
+    container->setPlugin(placeholder->plugin());
+
+    if (!placeholder->plugin()->initialize(container)) {

[Bernhard Bauer, 2015/01/30 14:12:56]

WebViewPlugin::initialize() always returns true, so this branch isn't necessary.
(Just DCHECK the return value?)

[tommycli, 2015/01/30 17:02:40]

Done.

+      // We couldn't initialize the new plug-in. Restore the old one and abort.
+      container->setPlugin(plugin_);
+      placeholder->plugin()->destroy();
+      delete this;
+      return;
+    }
+
+    placeholder->plugin()->RestoreTitleText();

[Bernhard Bauer, 2015/01/30 14:12:56]

This is probably also not necessary, because the plugin didn't have time to
change the title text :)

[tommycli, 2015/01/30 17:02:40]

Done.

+    container->invalidate();
+    container->reportGeometry();
+
+    delete this;
+  }
+}
+
+void PluginPreroller::OnThrottlerDestroyed() {
+  throttler_ = nullptr;
+  delete this;
+}