Support migrating multi-install Chrome to single-install.

chrome/installer/setup/install_worker.cc

Index: chrome/installer/setup/install_worker.cc
diff --git a/chrome/installer/setup/install_worker.cc b/chrome/installer/setup/install_worker.cc
index 64af4dad2d70914344cc963602cb0ccd6f3b8aac..1166dc7d3fe7126613dc8d6aca1da71528e7443b 100644
--- a/chrome/installer/setup/install_worker.cc
+++ b/chrome/installer/setup/install_worker.cc
@@ -1092,6 +1092,50 @@ void AddUsageStatsWorkItems(const InstallationState& original_state,
   }
 }
 
+// Migrates the usagestats value from the binaries to Chrome when migrating
+// multi-install Chrome to single-install.

[robertshield, 2015/01/23 22:45:30]

any reason not to do this separately first, or does it have to be coupled to the
multi->single migration?

[grt (UTC plus 2), 2015/01/24 02:25:16]

In the current world, usagestats is read from/written to only the binaries' key
for multi-install Chrome (and removed from Chrome's, if present) and read
from/written to only Chrome's key for single-install Chrome. I think it's
simpler to keep this logic, because we don't need to change the usagestats
handling in Chrome itself: multi-install still looks in the binaries' key,
single-install still looks in Chrome's. Happy to discuss further if you think
there's risk in this.

+void AddMigrateUsageStatesWorkItems(const InstallationState& original_state,
+                                    const InstallerState& installer_state,
+                                    WorkItemList* install_list) {
+  // This operation only applies to single-installs.

[robertshield, 2015/01/23 22:45:30]

nit: less ambiguous: This operation only applies when the this installer run is
updating or migrating to a single install.

Actually, that's too long.. anyway, maybe something to that effect?

[grt (UTC plus 2), 2015/01/24 02:25:15]

Reworded all comments here in the hopes that they are more clear. Let me know
what you think.

+  if (installer_state.is_multi_install())
+    return;
+
+  // This operation only applies to Chrome.
+  const Product* chrome_product =
+      installer_state.FindProduct(BrowserDistribution::CHROME_BROWSER);
+  if (!chrome_product) {
+    NOTREACHED();
+    return;
+  }
+
+  const ProductState* chrome_state = original_state.GetProductState(
+      installer_state.system_install(),
+      BrowserDistribution::CHROME_BROWSER);
+  // This operation only applies when updating multi-install Chrome to
+  // single-install.
+  if (!chrome_state || !chrome_state->is_multi_install())
+    return;
+
+  const ProductState* binaries_state = original_state.GetProductState(
+      installer_state.system_install(),
+      BrowserDistribution::CHROME_BINARIES);
+
+  // There is nothing to be done if the binaries do not have stats.
+  DWORD usagestats = 0;
+  if (!binaries_state || !binaries_state->GetUsageStats(&usagestats))
+    return;
+
+  // Write the value that was read to Chrome's ClientState key.
+  install_list->AddSetRegValueWorkItem(
+      installer_state.root_key(),
+      chrome_product->distribution()->GetStateKey(),
+      KEY_WOW64_32KEY,
+      google_update::kRegUsageStatsField,
+      usagestats,
+      true);
+}
+
 bool AppendPostInstallTasks(const InstallerState& installer_state,
                             const base::FilePath& setup_path,
                             const Version* current_version,
@@ -1310,6 +1354,16 @@ void AddInstallWorkItems(const InstallationState& original_state,
                             install_list);
   }
 
+  // Ensure that the Clients key for the binaries is gone for single installs.

[robertshield, 2015/01/23 22:45:30]

Do we need to double check to make sure this doesn't remove the last Clients key
mid-way triggering Omaha self-destruct?

[grt (UTC plus 2), 2015/01/24 02:25:15]

Line 1343 adds the Clients key for Chrome itself, so I don't think that's a
concern.

+  if (!installer_state.is_multi_install()) {
+    BrowserDistribution* binaries_dist =
+        BrowserDistribution::GetSpecificDistribution(
+            BrowserDistribution::CHROME_BINARIES);
+    install_list->AddDeleteRegKeyWorkItem(root,
+                                          binaries_dist->GetVersionKey(),
+                                          KEY_WOW64_32KEY);
+  }
+
   // TODO(huangs): Implement actual migration code and remove the hack below.
   // If installing Chrome without the legacy stand-alone App Launcher (to be
   // handled later), add "shadow" App Launcher registry keys so Google Update
@@ -1341,6 +1395,9 @@ void AddInstallWorkItems(const InstallationState& original_state,
   // Copy over brand, usagestats, and other values.
   AddGoogleUpdateWorkItems(original_state, installer_state, install_list);
 
+  // Migrate usagestats back to Chrome.
+  AddMigrateUsageStatesWorkItems(original_state, installer_state, install_list);
+
   // Append the tasks that run after the installation.
   AppendPostInstallTasks(installer_state,
                          setup_path,