Added proper extension manifest parser for launcher_page.

extensions/common/manifest_constants.cc

Index: extensions/common/manifest_constants.cc
diff --git a/extensions/common/manifest_constants.cc b/extensions/common/manifest_constants.cc
index 741bf2c6ac3379dfedb531393d11cd874fbf1ad7..b2c9d991e5fad41870fcd1b8d1b4207711237ec4 100644
--- a/extensions/common/manifest_constants.cc
+++ b/extensions/common/manifest_constants.cc
@@ -465,6 +465,9 @@ const char kInvalidKioskOnly[] =
     "Invalid value for 'kiosk_only'.";
 const char kInvalidKioskOnlyButNotEnabled[] =
     "The 'kiosk_only' key is set, but 'kiosk_enabled' is not set.";
+const char kInvalidLauncherPage[] = "Invalid value for 'launcher_page'.";
+const char kInvalidLauncherPagePage[] =
+    "Invalid value for 'launcher_page.page'.";
 const char kInvalidLaunchContainer[] =
     "Invalid value for 'app.launch.container'.";
 const char kInvalidLaunchValue[] =
@@ -666,6 +669,8 @@ const char kInsecureContentSecurityPolicy[] =
     " see http://developer.chrome.com/extensions/contentSecurityPolicy.html";
 const char kKeyIsDeprecatedWithReplacement[] =
     "Key \"*\" is deprecated.  Key \"*\" should be used instead.";
+const char kLauncherPagePageRequired[] =
+    "The 'launcher_page.page' key is required.";
 const char kLaunchPathAndExtentAreExclusive[] =
     "The 'app.launch.local_path' and 'app.urls' keys cannot both be set.";
 const char kLaunchPathAndURLAreExclusive[] =