Support for battery-savings meta element.

See:
https://github.com/chrishtr/battery-savings/blob/master/explainer.md

Bug: 1114184

Change-Id: I6772febbb0a511f523aab1bc34b2368695d7cad5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2343105Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795940}

third_party/blink/public/BUILD.gn

@@ -166,6 +166,7 @@ source_set("blink_headers") {
     "platform/web_audio_device.h",
     "platform/web_audio_latency_hint.h",
     "platform/web_audio_source_provider.h",
+    "platform/web_battery_savings.h",
     "platform/web_blob_info.h",
     "platform/web_cache.h",
     "platform/web_callbacks.h",

third_party/blink/public/platform/web_battery_savings.h

+// Copyright 2020 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.
+
+#ifndef THIRD_PARTY_BLINK_PUBLIC_PLATFORM_WEB_BATTERY_SAVINGS_H_
+#define THIRD_PARTY_BLINK_PUBLIC_PLATFORM_WEB_BATTERY_SAVINGS_H_
+
+namespace blink {
+
+// These are constants for the various keywords allowed for the battery-savings
+// meta element. For instance:
+//
+// <meta name="battery-savings" content="allow-reduced-frame-rate">
+//
+// These constants are bits which can be combined.
+enum WebBatterySavings {
+  kAllowReducedFrameRate = 1 << 0,
+  kAllowReducedScriptSpeed = 1 << 1,
+};
+
+using WebBatterySavingsFlags = unsigned;
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_PUBLIC_PLATFORM_WEB_BATTERY_SAVINGS_H_

third_party/blink/renderer/core/dom/document.cc

@@ -69,6 +69,7 @@
 #include "third_party/blink/public/mojom/ukm/ukm.mojom-blink.h"
 #include "third_party/blink/public/platform/platform.h"
 #include "third_party/blink/public/platform/task_type.h"
+#include "third_party/blink/public/platform/web_battery_savings.h"
 #include "third_party/blink/public/platform/web_content_settings_client.h"
 #include "third_party/blink/public/platform/web_theme_engine.h"
 #include "third_party/blink/public/web/web_print_page_description.h"
@@ -7013,6 +7014,32 @@ void Document::ColorSchemeMetaChanged() {
   GetStyleEngine().SetColorSchemeFromMeta(color_scheme);
 }
 
+void Document::BatterySavingsMetaChanged() {
+  if (!RuntimeEnabledFeatures::BatterySavingsMetaEnabled())
+    return;
+
+  if (!IsInMainFrame())
+    return;
+
+  auto* root_element = documentElement();
+  if (!root_element)
+    return;
+  for (HTMLMetaElement& meta_element :
+       Traversal<HTMLMetaElement>::DescendantsOf(*root_element)) {
+    if (EqualIgnoringASCIICase(meta_element.GetName(), "battery-savings")) {
+      SpaceSplitString split_content(
+          AtomicString(meta_element.Content().GetString().LowerASCII()));
+      WebBatterySavingsFlags savings = 0;
+      if (split_content.Contains("allow-reduced-framerate"))
+        savings |= kAllowReducedFrameRate;
+      if (split_content.Contains("allow-reduced-script-speed"))
+        savings |= kAllowReducedScriptSpeed;
+      GetPage()->GetChromeClient().BatterySavingsChanged(*GetFrame(), savings);
+      return;
+    }
+  }
+}
+
 static HTMLLinkElement* GetLinkElement(const Document* doc,
                                        bool (*match_fn)(HTMLLinkElement&)) {
   HTMLHeadElement* head = doc->head();

third_party/blink/renderer/core/dom/document.h

@@ -1545,6 +1545,10 @@ class CORE_EXPORT Document : public ContainerNode,
   // Update the presentation level color-scheme property for the root element.
   void ColorSchemeMetaChanged();
 
+  // A META element with name=battery-savings was added, removed, or modified.
+  // Re-collect the META values that apply and pass to LayerTreeHost.
+  void BatterySavingsMetaChanged();
+
   // Use counter related functions.
   void CountUse(mojom::WebFeature feature) final;
   void CountUse(mojom::WebFeature feature) const;

third_party/blink/renderer/core/frame/web_frame_widget_base.cc

@@ -1885,4 +1885,9 @@ void WebFrameWidgetBase::ForEachRemoteFrameControlledByWidget(
                                                callback);
 }
 
+void WebFrameWidgetBase::BatterySavingsChanged(WebBatterySavingsFlags savings) {
+  widget_base_->LayerTreeHost()->SetEnableFrameRateThrottling(
+      savings & kAllowReducedFrameRate);
+}
+
 }  // namespace blink

third_party/blink/renderer/core/frame/web_frame_widget_base.h

@@ -17,6 +17,7 @@
 #include "third_party/blink/public/mojom/manifest/display_mode.mojom-blink.h"
 #include "third_party/blink/public/mojom/page/widget.mojom-blink.h"
 #include "third_party/blink/public/platform/cross_variant_mojo_util.h"
+#include "third_party/blink/public/platform/web_battery_savings.h"
 #include "third_party/blink/public/platform/web_drag_data.h"
 #include "third_party/blink/public/web/web_frame_widget.h"
 #include "third_party/blink/renderer/core/clipboard/data_object.h"
@@ -490,6 +491,10 @@ class CORE_EXPORT WebFrameWidgetBase
   // level widget in a tab/window. E.g. a portal is activated or deactivated.
   void SetIsNestedMainFrameWidget(bool is_nested);
 
+  // The value of the applied battery-savings META element in the document
+  // changed.
+  void BatterySavingsChanged(WebBatterySavingsFlags savings);
+
  protected:
   enum DragAction { kDragEnter, kDragOver };
 

third_party/blink/renderer/core/html/html_meta_element.cc

@@ -484,6 +484,8 @@ void HTMLMetaElement::NameRemoved(const AtomicString& name_value) {
     GetDocument().GetFrame()->DidChangeThemeColor();
   } else if (EqualIgnoringASCIICase(name_value, "color-scheme")) {
     GetDocument().ColorSchemeMetaChanged();
+  } else if (EqualIgnoringASCIICase(name_value, "battery-savings")) {
+    GetDocument().BatterySavingsMetaChanged();
   }
 }
 
@@ -565,6 +567,10 @@ void HTMLMetaElement::ProcessContent() {
     GetDocument().ColorSchemeMetaChanged();
     return;
   }
+  if (EqualIgnoringASCIICase(name_value, "battery-savings")) {
+    GetDocument().BatterySavingsMetaChanged();
+    return;
+  }
 
   // All situations below require a content attribute (which can be the empty
   // string).

third_party/blink/renderer/core/loader/empty_clients.h

@@ -217,6 +217,8 @@ class CORE_EXPORT EmptyChromeClient : public ChromeClient {
   void SetCursorForPlugin(const ui::Cursor&, LocalFrame*) override {}
   void InstallSupplements(LocalFrame&) override {}
   void MainFrameScrollOffsetChanged(LocalFrame& main_frame) const override {}
+  void BatterySavingsChanged(LocalFrame& main_frame,
+                             WebBatterySavingsFlags savings) override {}
 };
 
 class CORE_EXPORT EmptyLocalFrameClient : public LocalFrameClient {

third_party/blink/renderer/core/page/chrome_client.h

@@ -39,6 +39,7 @@
 #include "third_party/blink/public/mojom/devtools/console_message.mojom-blink-forward.h"
 #include "third_party/blink/public/mojom/input/focus_type.mojom-blink-forward.h"
 #include "third_party/blink/public/platform/blame_context.h"
+#include "third_party/blink/public/platform/web_battery_savings.h"
 #include "third_party/blink/public/platform/web_float_rect.h"
 #include "third_party/blink/public/web/web_swap_result.h"
 #include "third_party/blink/public/web/web_widget_client.h"
@@ -519,6 +520,9 @@ class CORE_EXPORT ChromeClient : public GarbageCollected<ChromeClient> {
       LocalFrame* frame,
       std::unique_ptr<viz::DelegatedInkMetadata> metadata) {}
 
+  virtual void BatterySavingsChanged(LocalFrame& main_frame,
+                                     WebBatterySavingsFlags savings) = 0;
+
  protected:
   ChromeClient() = default;
 

third_party/blink/renderer/core/page/chrome_client_impl.cc

@@ -1245,4 +1245,12 @@ void ChromeClientImpl::SetDelegatedInkMetadata(
   frame->GetWidgetForLocalRoot()->SetDelegatedInkMetadata(std::move(metadata));
 }
 
+void ChromeClientImpl::BatterySavingsChanged(LocalFrame& main_frame,
+                                             WebBatterySavingsFlags savings) {
+  DCHECK(main_frame.IsMainFrame());
+  WebLocalFrameImpl::FromFrame(main_frame)
+      ->FrameWidgetImpl()
+      ->BatterySavingsChanged(savings);
+}
+
 }  // namespace blink

third_party/blink/renderer/core/page/chrome_client_impl.h

@@ -290,6 +290,9 @@ class CORE_EXPORT ChromeClientImpl final : public ChromeClient {
 
   double UserZoomFactor() const override;
 
+  void BatterySavingsChanged(LocalFrame& main_frame,
+                             WebBatterySavingsFlags savings) override;
+
  private:
   bool IsChromeClientImpl() const override { return true; }
 

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -239,6 +239,10 @@
       name: "BarcodeDetector",
       status: "stable",
     },
+    {
+      // https://github.com/chrishtr/battery-savings/blob/master/explainer.md
+      name: "BatterySavingsMeta",
+    },
     {
       // https://github.com/WICG/display-locking/blob/master/explainer-beforematch.md
       name: "BeforeMatchEvent",