Force migrate all clients from multi-install back to single-install.

chrome/installer/setup/installer_state.h

Index: chrome/installer/setup/installer_state.h
diff --git a/chrome/installer/setup/installer_state.h b/chrome/installer/setup/installer_state.h
index 9a5e9704e323760a379462f0cf693aa283e33980..2c25f3c1c0de7ff27c831cc4e71d26d96f32fc02 100644
--- a/chrome/installer/setup/installer_state.h
+++ b/chrome/installer/setup/installer_state.h
@@ -148,6 +148,10 @@ class InstallerState {
   // with the ClientState key we will be interacting with.
   BrowserDistribution::Type state_type() const { return state_type_; }
 
+  // Returns true if this is an update of multi-install Chrome to
+  // single-install.
+  bool is_migrating_to_single() const { return is_migrating_to_single_; }
+
   // Returns the BrowserDistribution instance corresponding to the binaries for
   // this run if we're operating on a multi-package product.
   BrowserDistribution* multi_package_binaries_distribution() const {
@@ -270,6 +274,7 @@ class InstallerState {
   bool msi_;
   bool background_mode_;
   bool verbose_logging_;
+  bool is_migrating_to_single_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InstallerState);