Android: Basic support for C++ in Android Studio

Add a new flag for generate_gradle.py, --native-target <gn target name>.
This allows C++ editing when --all is either passed or implicit (by
default). Starting with --native-target //chrome/android:monochrome in
Android Studio Canary (3.2) will result in most of the C++ files being
indexed and available both via the Android project view as well as the
double shift "search everywhere" box.

Switched maven URL to use "google()" instead, this works for all Android
Studio 3.0+, which covers all of stable/beta/canary.

Add specific AndroidManifest.xml to be used for the _all pseudo gradle
module since Android Studio now requires minSdk to not be specified in
the AndroidManifest.xml file.

Bug: 841529,827294,840368
Change-Id: Ifdee12bf7f9e7faf81cabf92dbf4c5613eb89996
Reviewed-on: https://chromium-review.googlesource.com/1053117
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557543}

• build/android/gradle/AndroidManifest.xml[Added - diff]
• build/android/gradle/android.jinja[diff]
• build/android/gradle/cmake.jinja[Added - diff]
• build/android/gradle/generate_gradle.py[diff]
• build/android/gradle/root.jinja[diff]