Add frameworks.jar for the Chromium WebView build

frameworks.jar contains the Android AOSP framework code.
This lets us build the Android WebView glue layer (frameworks/webview)
in the Chromium tree by building against the frameworks/base code
in frameworks.jar.

BUG=391488
R=mkosiba@chromium.org, rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/476173002

Cr-Commit-Position: refs/heads/master@{#289872}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289872 0039d316-1c4b-4281-b951-d872f2087c98

third_party/android_platform/README.chromium

@@ -9,7 +9,9 @@ License File: NOT_SHIPPED
 Security Critical: no
 
 Description:
-Android Platform engineering tools, specifically stack symbolization scripts.
+Android Platform engineering tools, specifically stack symbolization scripts
+and a jar containing the AOSP framework to build the Android WebView
+glue layer against.
 
 Local Modifications:
 Only picked the few scripts needed by chrome.