Update Android projects to API level 20.

This is required in order to roll chromium_revision to
keep up with Chrome, as third_party/android_tools have now
dropped support for API level 19.

Commands used:
third_party/android_tools/sdk/tools/android update project --name OpenSlDemo --target android-20 --path webrtc/examples/android/opensl_loopback
third_party/android_tools/sdk/tools/android update project --name WebRTCDemo --target android-20 --path webrtc/examples/android/media_demo/
third_party/android_tools/sdk/tools/android update project --name AppRTCDemo --target android-20 --path talk/examples/android/
Then I restored the changes of the ANDROID_SDK_ROOT -> ANDROID_HOME since it seems the Chromium build toolchain doesn't set it properly when
build/android/envsetup.sh is sourced.

BUG=
R=glaznev@webrtc.org, henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/23309004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7582 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/examples/android/project.properties

@@ -11,6 +11,6 @@
 #proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt
 
 # Project target.
-target=android-19
+target=android-20
 
 java.compilerargs=-Xlint:all -Werror

webrtc/examples/android/media_demo/build.xml

@@ -1,15 +1,92 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project name="WebRTCDemo" default="help">
+
+    <!-- The local.properties file is created and updated by the 'android' tool.
+         It contains the path to the SDK. It should *NOT* be checked into
+         Version Control Systems. -->
     <property file="local.properties" />
+
+    <!-- The ant.properties file can be created by you. It is only edited by the
+         'android' tool to add properties to it.
+         This is the place to change some Ant specific build properties.
+         Here are some properties you may want to change/update:
+
+         source.dir
+             The name of the source directory. Default is 'src'.
+         out.dir
+             The name of the output directory. Default is 'bin'.
+
+         For other overridable properties, look at the beginning of the rules
+         files in the SDK, at tools/ant/build.xml
+
+         Properties related to the SDK location or the project target should
+         be updated using the 'android' tool with the 'update' action.
+
+         This file is an integral part of the build system for your
+         application and should be checked into Version Control Systems.
+
+         -->
+    <property file="ant.properties" />
+
+    <!-- if sdk.dir was not set from one of the property file, then
+         get it from the ANDROID_HOME env var.
+         This must be done before we load project.properties since
+         the proguard config can use sdk.dir -->
     <property environment="env" />
     <condition property="sdk.dir" value="${env.ANDROID_SDK_ROOT}">
         <isset property="env.ANDROID_SDK_ROOT" />
     </condition>
+
+    <!-- The project.properties file is created and updated by the 'android'
+         tool, as well as ADT.
+
+         This contains project specific properties such as project target, and library
+         dependencies. Lower level build properties are stored in ant.properties
+         (or in .classpath for Eclipse projects).
+
+         This file is an integral part of the build system for your
+         application and should be checked into Version Control Systems. -->
     <loadproperties srcFile="project.properties" />
+
+    <!-- quick check on sdk.dir -->
     <fail
             message="sdk.dir is missing. Make sure to generate local.properties using 'android update project' or to inject it through the ANDROID_SDK_ROOT environment variable."
             unless="sdk.dir"
     />
+
+    <!--
+        Import per project custom build rules if present at the root of the project.
+        This is the place to put custom intermediary targets such as:
+            -pre-build
+            -pre-compile
+            -post-compile (This is typically used for code obfuscation.
+                           Compiled code location: ${out.classes.absolute.dir}
+                           If this is not done in place, override ${out.dex.input.absolute.dir})
+            -post-package
+            -post-build
+            -pre-clean
+    -->
     <import file="custom_rules.xml" optional="true" />
+
+    <!-- Import the actual build file.
+
+         To customize existing targets, there are two options:
+         - Customize only one target:
+             - copy/paste the target into this file, *before* the
+               <import> task.
+             - customize it to your needs.
+         - Customize the whole content of build.xml
+             - copy/paste the content of the rules files (minus the top node)
+               into this file, replacing the <import> task.
+             - customize to your needs.
+
+         ***********************
+         ****** IMPORTANT ******
+         ***********************
+         In all cases you must update the value of version-tag below to read 'custom' instead of an integer,
+         in order to avoid having your file be overridden by tools such as "android update project"
+    -->
+    <!-- version-tag: 1 -->
     <import file="${sdk.dir}/tools/ant/build.xml" />
+
 </project>

webrtc/examples/android/media_demo/project.properties

@@ -11,4 +11,4 @@
 #proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt
 
 # Project target.
-target=android-19
+target=android-20

webrtc/examples/android/opensl_loopback/project.properties

@@ -11,6 +11,6 @@
 #proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt
 
 # Project target.
-target=android-19
+target=android-20
 
 java.compilerargs=-Xlint:all -Werror