Reset user data directory and disk cache directory after downgrade.

chrome/installer/util/install_util.cc

Index: chrome/installer/util/install_util.cc
diff --git a/chrome/installer/util/install_util.cc b/chrome/installer/util/install_util.cc
index 8b6dfa75deab255b214ff5e749ab7e76949ad6a7..081f9e43ef7904c23b37b784ad1d9f1bb268cf2e 100644
--- a/chrome/installer/util/install_util.cc
+++ b/chrome/installer/util/install_util.cc
@@ -44,6 +44,7 @@ using installer::ProductState;
 
 namespace {
 
+const wchar_t kRegDowngradeVersion[] = L"DowngrdeVersion";
 const wchar_t kStageBinaryPatching[] = L"binary_patching";
 const wchar_t kStageBuilding[] = L"building";
 const wchar_t kStageConfiguringAutoLaunch[] = L"configuring_auto_launch";
@@ -627,6 +628,48 @@ bool InstallUtil::ProgramCompare::GetInfo(const base::File& file,
   return GetFileInformationByHandle(file.GetPlatformFile(), info) != 0;
 }
 
+// static
+base::Version InstallUtil::GetDowngradeVersion(HKEY root) {

[grt (UTC plus 2), 2016/05/19 23:39:28]

i think it's cleaner for this to take a bool system_install rather than the
HKEY. it should also take the const AppRegistrationData& as mentioned below

[zmin, 2016/05/20 00:52:25]

I use HKEY instead of bool here because
1) Make it same as the functions below. The AddDowngradeVersionItem function is
called in install_worker.cc which the root key is get directly from
installer_state.root_key().
2) This function is also called by AddDowngradeVersionItem(), using HKEY avoid
converting between bool and HKEY

[grt (UTC plus 2), 2016/05/20 15:25:05]

using HKEY leaks an implementation detail into the interface. why should
MoveUserDataForFirstRunAfterDowngrade need to know that the value is stored in
the registry, and know how to figure out which hive to look in? i think it's
fine if this takes a bool and the fn below takes an HKEY. also fine to to the
bool->HKEY here and down below. could also have the fn below take a const
InstallerState& and use its root_key() method, but that may make unittesting
more difficult.

[zmin, 2016/05/20 16:33:05]

Sure, I'll do bool for both.

+  base::win::RegKey key;
+  base::string16 downgrade_version;
+  if (key.Open(root,
+               BrowserDistribution::GetDistribution()->GetStateKey().c_str(),
+               KEY_QUERY_VALUE | KEY_WOW64_32KEY) != ERROR_SUCCESS ||
+      key.ReadValue(kRegDowngradeVersion, &downgrade_version) !=
+          ERROR_SUCCESS) {
+    return base::Version();
+  }
+  return base::Version(base::UTF16ToASCII(downgrade_version));
+}
+
+// static
+void InstallUtil::AddSetDowngradeVersionItem(

[grt (UTC plus 2), 2016/05/19 23:39:28]

this should take a const AppRegistrationData& as input rather than call
BrowserDistribution::GetDistribution(). same for below.

[zmin, 2016/05/20 00:52:25]

Done. But I'll use BrowserDistribution* which is a wrapper of
AppRegistrationData.

[grt (UTC plus 2), 2016/05/20 15:25:05]

Why? I think it'll be easier to unittest using ARD.

[zmin, 2016/05/20 16:33:05]

There is no much difference. BrowserDistribution->GetStateKey just simply call
ARD->GetStateKey. Unittest works fine with BrowserDistribution.

+    HKEY root,
+    const base::Version& existing_version,
+    WorkItemList* list) {
+  DCHECK(list);
+  if (!GetDowngradeVersion(root).IsValid()) {
+    list->AddSetRegValueWorkItem(
+        root, BrowserDistribution::GetDistribution()->GetStateKey(),
+        KEY_WOW64_32KEY, kRegDowngradeVersion,
+        base::ASCIIToUTF16(existing_version.GetString()), false);
+  }
+}
+
+// static
+void InstallUtil::AddRemoveDowngradeVersionItem(
+    HKEY root,
+    const base::Version& new_version,
+    WorkItemList* list) {
+  DCHECK(list);
+  base::Version downgrade_version = GetDowngradeVersion(root);
+  if (downgrade_version.IsValid() && downgrade_version <= new_version) {
+    list->AddDeleteRegValueWorkItem(
+        root, BrowserDistribution::GetDistribution()->GetStateKey(),
+        KEY_WOW64_32KEY, kRegDowngradeVersion);
+  }
+}
+
 InstallUtil::ProgramCompare::ProgramCompare(const base::FilePath& path_to_match)
     : ProgramCompare(path_to_match, ComparisonType::FILE) {}