Switching Clank to use direction-based selection granularity strategy and adding a chrome flag.

This will also be enabled on Aura when Aura and Android touch selection flows
finally unified. I also plan to have at least one more experimental strategy
implmenented.

Prerequisite CL: https://codereview.chromium.org/988023005/

BUG=451255

Review URL: https://codereview.chromium.org/1096773002

Cr-Commit-Position: refs/heads/master@{#326896}

chrome/app/generated_resources.grd

@@ -5876,6 +5876,18 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_TOUCH_EDITING_DESCRIPTION" desc="Description of the flag to enable touch based text editing.">
         Touch editing can be initiated by tapping on a textfield or a selected text.
       </message>
+      <message name="IDS_FLAGS_TOUCH_SELECTION_STRATEGY_NAME" desc="Name of the flag that controls touch based text selection strategy.">
+        Touch text selection strategy
+      </message>
+      <message name="IDS_FLAGS_TOUCH_SELECTION_STRATEGY_DESCRIPTION" desc="Description of the flag that controls touch based text selection strategy.">
+        Controls how text selection granularity changes when touch text selection handles are dragged. Non-default behavior is experimental.
+      </message>
+      <message name="IDS_TOUCH_SELECTION_STRATEGY_CHARACTER" desc="Description for the touch text selection strategy which always uses character granularity.">
+        Character
+      </message>
+      <message name="IDS_TOUCH_SELECTION_STRATEGY_DIRECTION" desc="Description for the touch text selection strategy which is based on the direction in which the handle is dragged.">
+        Direction
+      </message>
       <message name="IDS_FLAGS_WALLET_SERVICE_USE_SANDBOX_NAME" desc="Title for the flag to use the Online Wallet sandbox servers (instead of production).">
         Use Wallet sandbox servers
       </message>

chrome/browser/about_flags.cc

@@ -180,6 +180,16 @@ const Experiment::Choice kOverscrollHistoryNavigationChoices[] = {
 };
 #endif
 
+const Experiment::Choice kTouchTextSelectionStrategyChoices[] = {
+  { IDS_GENERIC_EXPERIMENT_CHOICE_DEFAULT, "", "" },
+  { IDS_TOUCH_SELECTION_STRATEGY_CHARACTER,
+    switches::kTouchTextSelectionStrategy,
+    "character" },
+  { IDS_TOUCH_SELECTION_STRATEGY_DIRECTION,
+    switches::kTouchTextSelectionStrategy,
+    "direction" }
+};
+
 #if !defined(DISABLE_NACL)
 const Experiment::Choice kNaClDebugMaskChoices[] = {
   // Secure shell can be used on ChromeOS for forwarding the TCP port opened by
@@ -1218,6 +1228,13 @@ const Experiment kExperiments[] = {
     ENABLE_DISABLE_VALUE_TYPE(switches::kEnableTouchEditing,
                               switches::kDisableTouchEditing)
   },
+  {
+      "touch-selection-strategy",
+      IDS_FLAGS_TOUCH_SELECTION_STRATEGY_NAME,
+      IDS_FLAGS_TOUCH_SELECTION_STRATEGY_DESCRIPTION,
+      kOsAndroid,   // TODO(mfomitchev): Add CrOS/Win/Linux support soon.
+      MULTI_VALUE_TYPE(kTouchTextSelectionStrategyChoices)
+  },
   {
     "enable-stale-while-revalidate",
     IDS_FLAGS_ENABLE_STALE_WHILE_REVALIDATE_NAME,

content/browser/renderer_host/render_process_host_impl.cc

@@ -1325,6 +1325,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kStatsCollectionController,
     switches::kTestType,
     switches::kTouchEvents,
+    switches::kTouchTextSelectionStrategy,
     switches::kTraceToConsole,
     // This flag needs to be propagated to the renderer process for
     // --in-process-webgl.

content/public/common/content_switches.cc

@@ -785,6 +785,11 @@ const char kTestingFixedHttpsPort[]         = "testing-fixed-https-port";
 // Type of the current test harness ("browser" or "ui").
 const char kTestType[]                      = "test-type";
 
+// Controls how text selection granularity changes when touch text selection
+// handles are dragged. Should be "character" or "direction". If not specified,
+// the platform default is used.
+const char kTouchTextSelectionStrategy[]    = "touch-selection-strategy";
+
 // Causes TRACE_EVENT flags to be recorded beginning with shutdown. Optionally,
 // can specify the specific trace categories to include (e.g.
 // --trace-shutdown=base,net) otherwise, all events are recorded.

content/public/common/content_switches.h

@@ -217,6 +217,7 @@ CONTENT_EXPORT extern const char kTabCaptureUpscaleQuality[];
 CONTENT_EXPORT extern const char kTestingFixedHttpPort[];
 CONTENT_EXPORT extern const char kTestingFixedHttpsPort[];
 CONTENT_EXPORT extern const char kTestType[];
+CONTENT_EXPORT extern const char kTouchTextSelectionStrategy[];
 CONTENT_EXPORT extern const char kTraceShutdown[];
 extern const char kTraceShutdownFile[];
 extern const char kTraceStartup[];

content/renderer/render_view_impl.cc

@@ -762,6 +762,25 @@ void RenderViewImpl::Initialize(const ViewMsg_New_Params& params,
   if (switches::IsTouchEditingEnabled())
     webview()->settings()->setTouchEditingEnabled(true);
 
+#if defined(OS_ANDROID)
+  WebSettings::SelectionStrategyType selection_strategy_default =
+      WebSettings::SelectionStrategyType::Direction;
+#else
+  WebSettings::SelectionStrategyType selection_strategy_default =
+      WebSettings::SelectionStrategyType::Character;
+#endif
+
+  WebSettings::SelectionStrategyType selection_strategy =
+      selection_strategy_default;
+  const std::string selection_strategy_str =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+          switches::kTouchTextSelectionStrategy);
+  if (selection_strategy_str == "character")
+    selection_strategy = WebSettings::SelectionStrategyType::Character;
+  else if (selection_strategy_str == "direction")
+    selection_strategy = WebSettings::SelectionStrategyType::Direction;
+  webview()->settings()->setSelectionStrategy(selection_strategy);
+
   if (!params.frame_name.empty())
     webview()->mainFrame()->setName(params.frame_name);
 

tools/metrics/histograms/histograms.xml

@@ -55340,6 +55340,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="593707592" label="disable-network-portal-notification"/>
   <int value="598827460" label="enable-roboto-font-ui"/>
   <int value="606288133" label="enable-print-preview-register-promos"/>
+  <int value="609112512" label="touch-selection-strategy"/>
   <int value="610545308" label="enable-potentially-annoying-security-features"/>
   <int value="625273056" label="disable-boot-animation"/>
   <int value="630947363" label="touch-events"/>