[Android WebView] Implement the capture picture API.

android_webview/common/render_view_messages.h

Index: android_webview/common/render_view_messages.h
diff --git a/android_webview/common/render_view_messages.h b/android_webview/common/render_view_messages.h
index 53b23f3e5a38057a1056bd0dd38bae04bc40b3dd..beb11320495e7a6b660cca6ec8a92e79da26d3f4 100644
--- a/android_webview/common/render_view_messages.h
+++ b/android_webview/common/render_view_messages.h
@@ -55,6 +55,10 @@ IPC_MESSAGE_ROUTED2(AwViewMsg_DoHitTest,
 IPC_MESSAGE_ROUTED1(AwViewMsg_EnableCapturePictureCallback,
                     bool /* enable */)
 
+// Requests a new picture with the latest renderer contents synchronously.
+// This message blocks the browser process on the renderer until complete.
+IPC_SYNC_MESSAGE_ROUTED0_0(AwViewMsg_CapturePictureSync)
+
 //-----------------------------------------------------------------------------
 // RenderView messages
 // These are messages sent from the renderer to the browser process.