Bug 770371 - Add a margin to the tappable area for copying selected text [r=margaret]

mobile/android/chrome/content/browser.js

@@ -1746,8 +1746,11 @@ var SelectionHandler = {
       win = win.parent;
     }
 
-    return (aX - offset.x > this.cache.rect.left && aX - offset.x < this.cache.rect.right) &&
-           (aY - offset.y > this.cache.rect.top && aY - offset.y < this.cache.rect.bottom);
+    let radius = ElementTouchHelper.getTouchRadius();
+    return (aX - offset.x > this.cache.rect.left - radius.left &&
+            aX - offset.x < this.cache.rect.right + radius.right &&
+            aY - offset.y > this.cache.rect.top - radius.top &&
+            aY - offset.y < this.cache.rect.bottom + radius.bottom);
   },
 
   // Returns true if the selection has been reversed. Takes optional aIsStartHandle
@@ -3623,6 +3626,19 @@ const ElementTouchHelper = {
     return elem;
   },
 
+  /* Returns the touch radius in content px. */
+  getTouchRadius: function getTouchRadius() {
+    let dpiRatio = ViewportHandler.displayDPI / kReferenceDpi;
+    let zoom = BrowserApp.selectedTab._zoom;
+    return {
+      top: this.radius.top * dpiRatio / zoom,
+      right: this.radius.right * dpiRatio / zoom,
+      bottom: this.radius.bottom * dpiRatio / zoom,
+      left: this.radius.left * dpiRatio / zoom
+    };
+  },
+
+  /* Returns the touch radius in reference pixels. */
   get radius() {
     let prefs = Services.prefs;
     delete this.radius;
@@ -3640,11 +3656,6 @@ const ElementTouchHelper = {
 
   /* Retrieve the closest element to a point by looking at borders position */
   getClosest: function getClosest(aWindowUtils, aX, aY) {
-    if (!this.dpiRatio)
-      this.dpiRatio = aWindowUtils.displayDPI / kReferenceDpi;
-
-    let dpiRatio = this.dpiRatio;
-
     let target = aWindowUtils.elementFromPoint(aX, aY,
                                                true,   /* ignore root scroll frame*/
                                                false); /* don't flush layout */
@@ -3657,11 +3668,8 @@ const ElementTouchHelper = {
       return target;
 
     target = null;
-    let zoom = BrowserApp.selectedTab._zoom;
-    let nodes = aWindowUtils.nodesFromRect(aX, aY, this.radius.top * dpiRatio / zoom,
-                                                   this.radius.right * dpiRatio / zoom,
-                                                   this.radius.bottom * dpiRatio / zoom,
-                                                   this.radius.left * dpiRatio / zoom, true, false);
+    let radius = this.getTouchRadius();
+    let nodes = aWindowUtils.nodesFromRect(aX, aY, radius.top, radius.right, radius.bottom, radius.left, true, false);
 
     let threshold = Number.POSITIVE_INFINITY;
     for (let i = 0; i < nodes.length; i++) {