Checkout this link:
https://www.dartlang.org/tools/editor/troubleshoot.html
"Launching Dart Editor"
Your Java version should have the same bit width as your Dart Editor version. For example, if you're using a 64-bit Dart Editor, then you should use 64-bit Java. Otherwise, you might see a message like this when you try to launch Dart Editor:
Failed to load the JNI shared library "C:\Program Files(x86)\Java\jre6\\bin\client\jvm.dll
To determine which version of Java you are running, do one of the following:
1-Go to CMD type java -version.
2-Go to Start -> Programs and Features.
Specifying the Java runtime
If necessary, you can specify the Java runtime that Dart Editor uses. Go to your Dart installation directory and add the following two lines to DartEditor.ini immediately before the existing ‑vmargs line:
-vm
/full/path/to/java
Important: On Windows, use double backslashes (\) as the directory separator:
-vm
c:\\bin\\java_jdk1.7.0\\bin\\javaw.exe
For example, DartEditor.ini might have:
-vm
/usr/local/buildtools/java/jdk-64/bin/java
-vmargs