Auto merge of #21730 - ferjm:android.gstreamer, r=paulrouget

Enable WebAudio on Android

- [X] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [X] These changes fix #21619

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python/servo/build_commands.py

@@ -13,8 +13,11 @@ import datetime
 import os
 import os.path as path
 import platform
-import sys
 import shutil
+import subprocess
+import sys
+import urllib
+import zipfile
 
 from time import time
 
@@ -396,6 +399,34 @@ class MachCommands(CommandBase):
             if not os.path.exists(aar_out_dir):
                 os.makedirs(aar_out_dir)
             env["AAR_OUT_DIR"] = aar_out_dir
+            # GStreamer and its dependencies use pkg-config and this flag is required
+            # to make it work in a cross-compilation context.
+            env["PKG_CONFIG_ALLOW_CROSS"] = '1'
+            # Build the name of the package containing all GStreamer dependencies
+            # according to the build target.
+            gst_lib = "gst-build-{}".format(self.config["android"]["lib"])
+            gst_lib_zip = "%s.zip" % gst_lib
+            gst_dir = os.path.join(base_path, "gstreamer")
+            gst_lib_path = os.path.join(base_path, gst_dir, gst_lib)
+            pkg_config_path = os.path.join(gst_lib_path, "pkgconfig")
+            env["PKG_CONFIG_PATH"] = pkg_config_path
+            if not os.path.exists(gst_lib_path):
+                # Download GStreamer dependencies if they have not already been downloaded
+                print("Downloading GStreamer dependencies")
+                gst_url = "https://github.com/servo/libgstreamer_android_gen/blob/master/out/%s?raw=true" % gst_lib_zip
+                urllib.urlretrieve(gst_url, gst_lib_zip)
+                zip_ref = zipfile.ZipFile(gst_lib_zip, "r")
+                zip_ref.extractall(gst_dir)
+                os.remove(gst_lib_zip)
+
+                # Change pkgconfig info to make all GStreamer dependencies point
+                # to the libgstreamer_android.so bundle.
+                for each in os.listdir(pkg_config_path):
+                    if each.endswith('.pc'):
+                        print("Setting pkgconfig info for %s" % each)
+                        pc = os.path.join(pkg_config_path, each)
+                        expr = "s#libdir=.*#libdir=%s#g" % gst_lib_path
+                        subprocess.call(["perl", "-i", "-pe", expr, pc])
 
         if very_verbose:
             print (["Calling", "cargo", "build"] + opts)