Use a shallow checkout for the Chromium webview.apk prebuilt

Change-Id: Ibe55ec9c2e80877da7de8ffaa0b68b19c5e54a63

default.xml

@@ -108,7 +108,7 @@
   <project path="external/cblas" name="platform/external/cblas" groups="pdk" />
   <project path="external/chromium-libpac" name="platform/external/chromium-libpac" groups="pdk-fs" />
   <project path="external/chromium-trace" name="platform/external/chromium-trace" groups="pdk" />
-  <project path="external/chromium-webview" name="platform/external/chromium-webview" groups="pdk" />
+  <project path="external/chromium-webview" name="platform/external/chromium-webview" groups="pdk" clone-depth="1" />
   <project path="external/clang" name="platform/external/clang" groups="pdk" />
   <project path="external/cmockery" name="platform/external/cmockery" groups="pdk-fs" />
   <project path="external/compiler-rt" name="platform/external/compiler-rt" groups="pdk" />