Allow component installers to specify a map of installer attributes.

components/component_updater/default_component_installer.h

Index: components/component_updater/default_component_installer.h
diff --git a/components/component_updater/default_component_installer.h b/components/component_updater/default_component_installer.h
index f728b431f5ce1b22ca62c9b1c2c1294ecc1c7639..8819c29053bf1b0390f0680600defd3ffda0958b 100644
--- a/components/component_updater/default_component_installer.h
+++ b/components/component_updater/default_component_installer.h
@@ -86,11 +86,15 @@ class ComponentInstallerTraits {
   // Returns the human-readable name of the component.
   virtual std::string GetName() const = 0;
 
-  // Returns the additional parameters to be used in the update checks for
-  // this component. A compatible server may use this attribute to negotiate
-  // special update rules when issuing an update response.
-  // The current implementation restricts ap to ^([-+_=a-zA-Z0-9]{0,256})$
-  virtual std::string GetAp() const = 0;
+  // Returns a container of name-value pairs representing arbitrary,
+  // installer-defined metadata.
+  // The installer metadata may be used in the update checks for this component.
+  // A compatible server may use these attributes to negotiate special update
+  // rules when issuing an update response.
+  // Valid values for the name part of an attribute match
+  // ^[-_a-zA-Z0-9]{1,256}$ and valid values the value part of an attribute
+  // match ^[-.,;+_=a-zA-Z0-9]{0,256}$ .
+  virtual update_client::InstallerAttributes GetInstallerAttributes() const = 0;
 };
 
 // A DefaultComponentInstaller is intended to be final, and not derived from.