* Update dartdoc to v0.18.1 and fix API readme, borrowing from docs.flutter.io

Changes since last roll:
```
ec1e96864 Revert pub roll from recent dart roll. (#4904)
ac552fba4 Port flutter content handler to FIDL2. (#4903)
94cdd8103 Roll dart. (#4902)
af63732de Support `Path.addCircle` (#4783)
564c6a5a9 Add hint to use ninja with goma (#4894)
```
```

Includes:
* libtxt: move to the next run if the current run ends before the start of the line block (flutter/engine#4891)
* Rolled Dart SDK to e3051175192c83fafa3636c0f16d804734bb285a (flutter/engine#4877)

Revert "Make sure `flutter update-packages --verify-only` has a non-zero exit code (#15962)" (#16089)

This reverts commit cfda7a65.

* make sure --verify-only logs error messages and fix typo

* ensure non zero exit code

* undo random pubspec change

Fixes https://github.com/flutter/flutter/issues/14864

* add simple test case for passing shadow color through physical layer

* Update physical_model_test.dart

add newline

* AppBar accepts custom PageRoute

* remove unused import

* update AUTHORS

It's required to be set before we detect local engine.

Was broken by #15984

add --buildNumber and --buildName to flutter build like
flutter build apk --buildNumber=42 --buildName=1.0.42

Paying off technical debt...

This reverts commit 1f5d9041.

* Let iOS auto-signing tool handle Googler scenario

* Forgot to update tests

* Revert "Roll engine to 6473f1b106485cb0b4ea569af383173daeef8895 (#16032)"

This reverts commit 844ced01.

* Revert "Let travis test archiving per commit too (#16004)"

This reverts commit df5905f3.

Includes:
* Use newer Skia API for constructing mask blur filters (flutter/engine#4875)
* Retry fixing vulkan include (flutter/engine#4874)

Follow-up comments to #15984

* Revert "Revert "Move mockito to 3.0.0-alpha. (#15949)" (#15979)"

This reverts commit e59651f9.

* More thenReturn to thenAnswer when mocking Futures

* Revert "More thenReturn to thenAnswer when mocking Futures"

This reverts commit 194d2cf41754ad171efd6bb5898cf73bce5a75ab as we are reverting engine roll.

* Revert "Revert "More thenReturn to thenAnswer when mocking Futures""

This reverts commit 52c9e96b304b220f66d78a252fccea0c8e0ef24c.

* Add dependency override

* Fix issue

This updates AppContext per the recommendations in #15352

Fixes #15352

* Support for decimal and signed numeric keyboard

* Comments

* Rebase.

* Roll engine to dd6f46c485192f4506035088c9065b9f5dbba9ab

Type-related fixes in flutter_driver and fuchsia_remote_debug_protocol
tests.

Includes:
* Remove declaration for undefined GPUSurfaceGL::SelectPixelConfig (flutter/engine#4857)
* Vulkan swap chain setup no longer uses GrPixelConfig and doesn't incl…
* Revert dart roll 20180322 (flutter/engine#4855)
* Roll back pub upgrade. (flutter/engine#4854)
* Roll flutter 20180322a (flutter/engine#4852)
* Document Window.defaultRouteName a little better. (flutter/engine#4851)
* Roll dart to 95e9e890a9 (flutter/engine#4850)

Includes:
* Fix GPUSurfaceGL includes on Linux (flutter/engine#4849)
* Slightly improve the docs for the internal _futurize method (flutter/engine#4847)
* Fix supported color type check on iOS simulators (flutter/engine#4846)
* Fix GPUSurfaceGL includes on macOS (flutter/engine#4844)
* Handle Apple-specific GLES headers (flutter/engine#4843)
* [fuchsia] Fix up includes of Zircon headers (flutter/engine#4842)
* VulkanSurface and GPUSurfaceGL no longer use GrPixelConfig (flutter/engine#4814)

Includes:
* Roll Skia (flutter/engine#4841)

Includes:
* Provide asset lookup key on ios (flutter/engine#4817)
* Load kernel files from the script URI in the isolate create callback (flutter/engine#4828)
* Remove some unneeded profiling flags (flutter/engine#4827)
* Remove the canvas save/restore calls in Paragraph::Paint (flutter/engine#4822)

This caused a test failure in the integration_ui_ios devicelab test.

```
stdout: [   +3 ms] 00:02 [32m+0[0m: end-to-end test Ensure keyboard dismissal resizes the view to original size[0m
stdout: [+8129 ms] 00:11 [32m+0[0m[31m -1[0m: end-to-end test Ensure keyboard dismissal resizes the view to original size [1m[31m[E][0m[0m
stdout: [   +5 ms]   DriverError: Failed to fulfill Tap: Flutter application not responding
stdout: [        ]   Original error: TimeoutException after 0:00:07.500000: Future not completed
stdout: [        ]   Original stack trace:
stdout: [        ]   #0      FlutterDriver._sendCommand (package:flutter_driver/src/driver/driver.dart:324:18)
stdout: [        ]
stdout: [        ]   #1      FlutterDriver.tap (package:flutter_driver/src/driver/driver.dart:368:11)
stdout: [        ]
stdout: [        ]   #2      main.. (file:///[... snip ...]/flutter/dev/integration_tests/ui/test_driver/keyboard_resize_test.dart:34:20)
```

This reverts commit 067be92a.

This reverts commit a7e62258 as there are failing tests.

* Move mockito to 3.0.0-alpha.

This is needed so it matches mockito version used internally.

* Pick up +2 for the fixes

* Fix whenReturn in fuchsia_remote_debug_protocol

* more thenReturn becomes thenAnswer

* more thenReturn becomes thenAnswer

* more thenReturn becomes thenAnswer

Roll engine to version dd6f46c485192f4506035088c9065b9f5dbba9ab