[Instant Start] Ignore background time in TabSwitcherOnReturn=Immediate

When TabSwitcherOnReturn is set to "Immediate", the tab switcher should
show up immediately regardless of whether the last background timestamp
is available or not.

"Immediate" is a setting for dev testing only.

Bug: 1016952
Change-Id: I3ac40d6695089ea9b14e3841b8834ae3a6b44b7c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1877812Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708934}

chrome/android/java/src/org/chromium/chrome/browser/tasks/ReturnToChromeExperimentsUtil.java

@@ -37,14 +37,14 @@ public final class ReturnToChromeExperimentsUtil {
      * @return true if past threshold, false if not past threshold or experiment cannot be loaded.
      */
     public static boolean shouldShowTabSwitcher(final long lastBackgroundedTimeMillis) {
-        if (lastBackgroundedTimeMillis == -1) {
-            // No last background timestamp set, use control behavior.
-            return false;
-        }
-
         int tabSwitcherAfterMillis = ChromeFeatureList.getFieldTrialParamByFeatureAsInt(
                 ChromeFeatureList.TAB_SWITCHER_ON_RETURN, TAB_SWITCHER_ON_RETURN_MS, -1);
 
+        if (lastBackgroundedTimeMillis == -1) {
+            // No last background timestamp set, use control behavior unless "immediate" was set.
+            return tabSwitcherAfterMillis == 0;
+        }
+
         if (tabSwitcherAfterMillis < 0) {
             // If no value for experiment, use control behavior.
             return false;

chrome/android/javatests/src/org/chromium/chrome/browser/tasks/ReturnToChromeTest.java

@@ -55,7 +55,7 @@ public class ReturnToChromeTest {
     public void setUp() {
         FeatureUtilities.setGridTabSwitcherEnabledForTesting(true);
 
-        mActivityTestRule.startMainActivityFromLauncher();
+        mActivityTestRule.startMainActivityOnBlankPage();
         mActivity = mActivityTestRule.getActivity();
 
         setupTabs();

chrome/test/android/javatests/src/org/chromium/chrome/test/BottomSheetTestRule.java

@@ -113,8 +113,7 @@ public class BottomSheetTestRule extends ChromeTabbedActivityTestRule {
         setSheetState(mStartingBottomSheetState, /* animate = */ false);
     }
 
-    public void startMainActivityOnBottomSheet(@BottomSheet.SheetState int startingSheetState)
-            throws InterruptedException {
+    public void startMainActivityOnBottomSheet(@BottomSheet.SheetState int startingSheetState) {
         mStartingBottomSheetState = startingSheetState;
         startMainActivityOnBlankPage();
     }
@@ -124,7 +123,7 @@ public class BottomSheetTestRule extends ChromeTabbedActivityTestRule {
     // ActivityTestRule interface. To work round this override the methods that start activities.
     // See https://crbug.com/726444.
     @Override
-    public void startMainActivityOnBlankPage() throws InterruptedException {
+    public void startMainActivityOnBlankPage() {
         super.startMainActivityOnBlankPage();
         afterStartingActivity();
     }

chrome/test/android/javatests/src/org/chromium/chrome/test/ChromeActivityTestRule.java

@@ -400,7 +400,7 @@ public class ChromeActivityTestRule<T extends ChromeActivity> extends ActivityTe
      * Starts the Main activity and open a blank page.
      * This is faster and less flakyness-prone than starting on the NTP.
      */
-    public void startMainActivityOnBlankPage() throws InterruptedException {
+    public void startMainActivityOnBlankPage() {
         startMainActivityWithURL("about:blank");
     }