cros: Add a chrome flag for touchable app context menus.

Add a chrome flag so users can enable the feature without using a
switch.

BUG=832876

Change-Id: I18b754c892e37e995561bd22b6e95545683ff03e
Reviewed-on: https://chromium-review.googlesource.com/1012930Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555731}

chrome/browser/about_flags.cc

@@ -1527,6 +1527,10 @@ const FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kEasyUnlockPromotionsName,
      flag_descriptions::kEasyUnlockPromotionsDescription, kOsCrOS,
      FEATURE_VALUE_TYPE(features::kEasyUnlockPromotions)},
+    {"enable-touchable-app-context-menu",
+     flag_descriptions::kTouchableAppContextMenuName,
+     flag_descriptions::kTouchableAppContextMenuDescription, kOsCrOS,
+     FEATURE_VALUE_TYPE(features::kTouchableAppContextMenu)},
     {
         "enable-pinch", flag_descriptions::kPinchScaleName,
         flag_descriptions::kPinchScaleDescription, kOsLinux | kOsWin | kOsCrOS,

chrome/browser/flag_descriptions.cc

@@ -1648,6 +1648,11 @@ const char kTouchAdjustmentDescription[] =
     "Refine the position of a touch gesture in order to compensate for touches "
     "having poor resolution compared to a mouse.";
 
+const char kTouchableAppContextMenuName[] = "Touchable App Context Menu";
+const char kTouchableAppContextMenuDescription[] =
+    "Enable the touchable app context menu, which enlarges app context menus "
+    "in the Launcher and Shelf to make room for new features.";
+
 const char kTouchDragDropName[] = "Touch initiated drag and drop";
 const char kTouchDragDropDescription[] =
     "Touch drag and drop can be initiated through long press on a draggable "

chrome/browser/flag_descriptions.h

@@ -1011,6 +1011,9 @@ extern const char kTopSitesFromSiteEngagementDescription[];
 extern const char kTouchAdjustmentName[];
 extern const char kTouchAdjustmentDescription[];
 
+extern const char kTouchableAppContextMenuName[];
+extern const char kTouchableAppContextMenuDescription[];
+
 extern const char kTouchDragDropName[];
 extern const char kTouchDragDropDescription[];
 

tools/metrics/histograms/enums.xml

@@ -27592,6 +27592,7 @@ from previous Chrome versions.
   <int value="834033186" label="enable-data-reduction-proxy-dev"/>
   <int value="834326277" label="enable-answers-in-suggest"/>
   <int value="835018878" label="disable-quic"/>
+  <int value="836406476" label="EnableTouchableAppContextMenu:enabled"/>
   <int value="838887742" label="manual-enhanced-bookmarks"/>
   <int value="841276069" label="ChromeHomeDoodle:disabled"/>
   <int value="841343322" label="disable-new-korean-ime"/>
@@ -27819,6 +27820,7 @@ from previous Chrome versions.
   <int value="1320201920" label="enable-touchpad-three-finger-click"/>
   <int value="1330264457" label="OmniboxUIExperimentVerticalLayout:disabled"/>
   <int value="1333847867" label="NoScriptPreviews:enabled"/>
+  <int value="1338864675" label="EnableTouchableAppContextMenu:disabled"/>
   <int value="1339426771" label="TopSitesFromSiteEngagement:disabled"/>
   <int value="1340690624" label="WebPaymentsMethodSectionOrderV2:disabled"/>
   <int value="1344833841" label="ImeThread:enabled"/>