[Devtools]: Proposal to change chart scale of the graph in memory section

allow to change chart scale of the graph on the memory usage section

this is how it currently looks like


from such graph it's really hard to see the change of one particular parameter

zooming the page somewhat helps but:
* the bottom of the page becomes unreachable, as it doesn't allow you scroll
* the values are cutted out and you see fewer of them


flutter doctor -v

```
[✓] Flutter (Channel nt4f04und, 2.1.0-12.0.pre, on Microsoft Windows [Version 10.0.19041.867], locale ru-RU)
• Flutter version 2.1.0-12.0.pre at c:\dev\src\flutter
• Framework revision 698d438960 (5 days ago), 2021-03-09 07:53:21 +0100
• Engine revision 2441c476a6
• Dart version 2.13.0 (build 2.13.0-116.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
• Android SDK at C:\Users\danya\AppData\Local\Android\sdk
• Platform android-30, build-tools 30.0.2
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
• All Android licenses accepted.

[✓] Chrome - develop for the web
• Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[!] Visual Studio - develop for Windows (Visual Studio Community 2019 16.7.7)
• Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
• Visual Studio Community 2019 version 16.7.30621.155
• Windows 10 SDK version 10.0.18362.0
✗ Visual Studio is missing necessary components. Please re-run the Visual Studio installer for the "Desktop
development with C++" workload, and include these components:
MSVC v142 - VS 2019 C++ x64/x86 build tools
- If there are multiple build tool versions available, install the latest
C++ CMake tools for Windows
Windows 10 SDK

[✓] Android Studio (version 4.0)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin version 50.0.1
• Dart plugin version 193.7547
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[✓] VS Code (version 1.54.2)
• VS Code at C:\Users\danya\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 3.20.0

[✓] Connected device (4 available)
• Redmi Note 5 (mobile) • 40c9f14 • android-arm64 • Android 9 (API 28)
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [Version 10.0.19041.867]
• Chrome (web) • chrome • web-javascript • Google Chrome 89.0.4389.82
• Edge (web) • edge • web-javascript • Microsoft Edge 89.0.774.50

! Doctor found issues in 1 category.
```

Start by locating the DevTools memory usage graph entry point and reviewing how its chart scale and page scrolling currently work. Reproduce the issue using the screenshots and verify that the graph can show smaller changes while keeping values visible and the bottom of the page reachable.

索引モデルが issue の本文から書いたものです。