Update Android target sdk verion

Update Android target sdk version from 19 to 21 to fit upgraded
xwalk_core_library.

BUG=XWALK-3234

Author: fujunwei

framework/project.properties

@@ -10,7 +10,7 @@
 # Indicates whether an apk should be generated for each density.
 split.density=false
 # Project target.
-target=android-19
+target=android-21
 apk-configurations=
 renderscript.opt.level=O0
 android.library=true

test/AndroidManifest.xml

@@ -47,7 +47,7 @@
     <uses-permission android:name="android.permission.GET_ACCOUNTS" />
     <uses-permission android:name="android.permission.BROADCAST_STICKY" />
 
-    <uses-sdk android:minSdkVersion="10" android:targetSdkVersion="19"/>
+    <uses-sdk android:minSdkVersion="10" android:targetSdkVersion="21"/>
 
     <instrumentation
         android:name="android.test.InstrumentationTestRunner"

test/project.properties

@@ -8,5 +8,5 @@
 # project structure.
 
 # Project target.
-target=android-19
+target=android-21
 android.library.reference.1=../framework