Enable touch drag-and-drop in WebUI tab strip

Touch drag-and-drop is enabled or disabled through WebPreferences
instead of a switch check in the renderer. The setting defaults to
the switch state but can be overridden.

The WebUI tab strip enables it always.

Bug: 229301
Change-Id: Ie3be6167f3c3c5d1fe21beb0238d6b2e0bdf05fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2270848Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788679}

chrome/browser/ui/webui/tab_strip/chrome_content_browser_client_tab_strip_part.cc

@@ -36,4 +36,5 @@ void ChromeContentBrowserClientTabStripPart::OverrideWebkitPrefs(
   web_prefs->minimum_font_size = default_prefs.minimum_font_size;
   web_prefs->minimum_logical_font_size =
       default_prefs.minimum_logical_font_size;
+  web_prefs->touch_drag_drop_enabled = true;
 }

content/public/common/common_param_traits_macros.h

@@ -247,6 +247,7 @@ IPC_STRUCT_TRAITS_BEGIN(content::WebPreferences)
   IPC_STRUCT_TRAITS_MEMBER(lazy_image_first_k_fully_load)
   IPC_STRUCT_TRAITS_MEMBER(allow_mixed_content_upgrades)
   IPC_STRUCT_TRAITS_MEMBER(always_show_focus)
+  IPC_STRUCT_TRAITS_MEMBER(touch_drag_drop_enabled)
 IPC_STRUCT_TRAITS_END()
 
 IPC_STRUCT_TRAITS_BEGIN(blink::mojom::WindowFeatures)

content/public/common/web_preferences.cc

@@ -8,9 +8,21 @@
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "third_party/blink/public/web/web_settings.h"
+#include "ui/base/ui_base_switches_util.h"
 
 using blink::WebSettings;
 
+namespace {
+
+bool IsTouchDragDropEnabled() {
+  // Cache the enabled state so it isn't queried on every WebPreferences
+  // creation. Note that this means unit tests can't override the state.
+  static const bool enabled = switches::IsTouchDragDropEnabled();
+  return enabled;
+}
+
+}  // namespace
+
 namespace content {
 
 // "Zyyy" is the ISO 15924 script code for undetermined script aka Common.
@@ -228,7 +240,8 @@ WebPreferences::WebPreferences()
       network_quality_estimator_web_holdback(
           net::EFFECTIVE_CONNECTION_TYPE_UNKNOWN),
       allow_mixed_content_upgrades(true),
-      always_show_focus(false) {
+      always_show_focus(false),
+      touch_drag_drop_enabled(IsTouchDragDropEnabled()) {
   standard_font_family_map[kCommonScript] =
       base::ASCIIToUTF16("Times New Roman");
   fixed_font_family_map[kCommonScript] = base::ASCIIToUTF16("Courier New");

content/public/common/web_preferences.h

@@ -360,6 +360,10 @@ struct CONTENT_EXPORT WebPreferences {
   // forcing :focus-visible to match regardless of focus method).
   bool always_show_focus;
 
+  // Whether touch input can trigger HTML drag-and-drop operations. The
+  // default value depends on the platform.
+  bool touch_drag_drop_enabled;
+
   // We try to keep the default values the same as the default values in
   // chrome, except for the cases where it would require lots of extra work for
   // the embedder to use the same default value.

content/renderer/render_view_impl.cc

@@ -351,9 +351,6 @@ void ApplyCommandLineToSettings(WebSettings* settings) {
   settings->SetThreadedScrollingEnabled(
       !command_line.HasSwitch(switches::kDisableThreadedScrolling));
 
-  if (switches::IsTouchDragDropEnabled())
-    settings->SetTouchDragDropEnabled(true);
-
   WebSettings::SelectionStrategyType selection_strategy;
   if (command_line.GetSwitchValueASCII(switches::kTouchTextSelectionStrategy) ==
       "direction")
@@ -954,6 +951,8 @@ void RenderView::ApplyWebPreferences(const WebPreferences& prefs,
     NOTREACHED();
   }
 
+  settings->SetTouchDragDropEnabled(prefs.touch_drag_drop_enabled);
+
 #if defined(OS_MACOSX)
   web_view->SetMaximumLegibleScale(prefs.default_maximum_page_scale_factor);
 #endif