Alter backoff behavior in India trigger experiment

This CL changes the backoff behavior from "backoff after N consecutive
declines/ignores" to "backoff after N declines/ignores unless accepted
once"

Bug: 840367
Change-Id: I18d3d1ac10da566d55950a62f705dc1da3efa587
Reviewed-on: https://chromium-review.googlesource.com/1208711Reviewed-by: Michael Martis <martis@chromium.org>
Commit-Queue: anthonyvd <anthonyvd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589161}

components/translate/core/browser/translate_manager_unittest.cc

@@ -491,6 +491,13 @@ TEST_F(TranslateManagerTest,
   EXPECT_THAT(histogram_tester.GetAllSamples(kInitiationStatusName),
               ElementsAre(Bucket(INITIATION_STATUS_SHOW_INFOBAR, 2),
                           Bucket(INITIATION_STATUS_SHOW_ICON, 2)));
+
+  // Initiating Translation again should still show the UI because accepting
+  // once prevents backoff from occurring moving forward.
+  translate_manager_->InitiateTranslation("en");
+  EXPECT_THAT(histogram_tester.GetAllSamples(kInitiationStatusName),
+              ElementsAre(Bucket(INITIATION_STATUS_SHOW_INFOBAR, 3),
+                          Bucket(INITIATION_STATUS_SHOW_ICON, 3)));
 }
 
 TEST_F(TranslateManagerTest, ShouldHonorExperimentRankerEnforcement_Enforce) {

components/translate/core/browser/translate_prefs.cc

@@ -839,13 +839,14 @@ int TranslatePrefs::GetForceTriggerOnEnglishPagesCount() const {
 
 void TranslatePrefs::ReportForceTriggerOnEnglishPages() {
   int current_count = GetForceTriggerOnEnglishPagesCount();
+  if (current_count != -1)
     prefs_->SetInteger(kForceTriggerTranslateCount, current_count + 1);
 }
 
 void TranslatePrefs::ReportAcceptedAfterForceTriggerOnEnglishPages() {
   int current_count = GetForceTriggerOnEnglishPagesCount();
-  if (current_count > 0)
-    prefs_->SetInteger(kForceTriggerTranslateCount, current_count - 1);
+  if (current_count != -1)
+    prefs_->SetInteger(kForceTriggerTranslateCount, -1);
 }
 
 // static

components/translate/core/browser/translate_prefs.h

@@ -307,9 +307,10 @@ class TranslatePrefs {
   // kOverrideTranslateTriggerInIndia experiment made translate trigger on an
   // English page when it otherwise wouldn't have.
   void ReportForceTriggerOnEnglishPages();
-  // Decrements the pref that represents how often the
+  // Sets to -1 the pref that represents how often the
   // kOverrideTranslateTriggerInIndia experiment made translate trigger on an
-  // English page when it otherwise wouldn't have.
+  // English page when it otherwise wouldn't have. This is a special value that
+  // signals that the backoff should not happen for that user.
   void ReportAcceptedAfterForceTriggerOnEnglishPages();
 
   // Migrate the sites blacklist from a list to a dictionary that maps sites