Experiment with emulating mouse hover with touch hover capable devices

We enable the hover feature on touchscreens on Samsung Galaxy S4, S5 by
turning on a hover feature switch, which simulated a mouse over event.

BUG=418188

Review URL: https://codereview.chromium.org/687323002

Cr-Commit-Position: refs/heads/master@{#306704}

chrome/app/generated_resources.grd

@@ -15286,6 +15286,13 @@ Do you accept?
       <message name="IDS_HOTWORD_NOTIFICATION_BUTTON" desc="The text displayed on the button of the hotword notification. ">
         Enable "Ok Google"
       </message>
+
+      <message name="IDS_FLAGS_ENABLE_TOUCH_HOVER_NAME" desc="Name of the 'Enable support for hover capable touchscreens' flag.">
+        Enable support for hover capable touchscreens.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_TOUCH_HOVER_DESCRIPTION" desc="Description of the 'Enable support for hover capable touchscreens' flag.">
+        Enables hover feature by holding your finger just over the screen to experience a mouseover event.
+      </message>
     </messages>
   </release>
 </grit>

chrome/browser/about_flags.cc

@@ -2050,6 +2050,13 @@ const Experiment kExperiments[] = {
     SINGLE_VALUE_TYPE(switches::kEnableSeccompFilterSandbox)
   },
 #endif
+  {
+    "enable-touch-hover",
+    IDS_FLAGS_ENABLE_TOUCH_HOVER_NAME,
+    IDS_FLAGS_ENABLE_TOUCH_HOVER_DESCRIPTION,
+    kOsAndroid,
+    SINGLE_VALUE_TYPE("enable-touch-hover")
+  },
 
   // NOTE: Adding new command-line switches requires adding corresponding
   // entries to enum "LoginCustomFlags" in histograms.xml. See note in

content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java

@@ -513,6 +513,9 @@ public class ContentViewCore
     // A ViewAndroidDelegate that delegates to the current container view.
     private ContentViewAndroidDelegate mViewAndroidDelegate;
 
+    // A flag to determine if we enable hover feature or not.
+    private Boolean mEnableTouchHover;
+
     /**
      * Constructs a new ContentViewCore. Embedders must call initialize() after constructing
      * a ContentViewCore and before using it.
@@ -1608,6 +1611,15 @@ public class ContentViewCore
      */
     public boolean onHoverEvent(MotionEvent event) {
         TraceEvent.begin("onHoverEvent");
+        // TODO(lanwei): Remove this switch once experimentation is complete -
+        // crbug.com/418188
+        if (event.getToolType(0) == MotionEvent.TOOL_TYPE_FINGER) {
+            if (mEnableTouchHover == null) {
+                mEnableTouchHover =
+                        CommandLine.getInstance().hasSwitch(ContentSwitches.ENABLE_TOUCH_HOVER);
+            }
+            if (!mEnableTouchHover.booleanValue()) return false;
+        }
         MotionEvent offset = createOffsetMotionEvent(event);
         try {
             if (mBrowserAccessibilityManager != null) {

content/public/android/java/src/org/chromium/content/common/ContentSwitches.java

@@ -70,6 +70,9 @@ public abstract class ContentSwitches {
     public static final String FORCE_DEVICE_SCALE_FACTOR =
             "force-device-scale-factor";
 
+    // Enable mouse hover emulation by holding your finger just over the screen.
+    public static final String ENABLE_TOUCH_HOVER = "enable-touch-hover";
+
     // Prevent instantiation.
     private ContentSwitches() {}
 }

tools/metrics/histograms/histograms.xml

@@ -49102,6 +49102,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1966730288" label="disable-threaded-compositing"/>
   <int value="1969604362" label="enable-pinch-virtual-viewport"/>
   <int value="1980011075" label="debug-packed-apps"/>
+  <int value="2000091128" label="enable-touch-hover"/>
   <int value="2004829262" label="enable-webgl-draft-extensions"/>
   <int value="2037756154" label="enable-impl-side-painting"/>
   <int value="2059322877" label="new-avatar-menu"/>